yacht battery life

How Long Do Marine Batteries Last? Tips To Extend Their Life

Marine batteries are one of the most important parts of your boat, so it’s essential to know how long they last and how to extend their lifespan. However, there are 4 different kinds of marine batteries. Each of which have different lifespans and different ways of extending their life.

On average, marine batteries last 3-5 years. However, they can last up to 10 years depending on the type of battery and how well they were maintained. Lithium marine batteries last 8-10 years, AGM last 4-7 years, gel cell and wet cell (flooded) last 2-5 years.

If we look at lifespan based on different marine battery types, here’s how it looks:

Note: A charge cycle represents a complete charge and discharge of a battery. Generally, marine batteries aren’t fully discharged and charged, so a full charge cycle is usually equal to many partial drains and charges.

Correctly maintaining and not misusing your battery are the most important things to do in order to extend its life expectancy. For example, AGM batteries can last 3-6 years longer if you properly maintain them. Continue reading to find out all you’ll need to know about taking care of your marine batteries.

Table of Contents

Marine battery basics

Before we get into more about marine battery details, let me first lay out some basic battery information to help you understand what I’m talking about. Most marine batteries are a mix of a starting battery (also referred to as a cranking battery) and a deep-cycle battery. ( source )

Starting batteries start your engine, and deep-cycle is what keeps your boat operating. There are specific batteries that fall into only those categories, but in this article I am referring to dual-purpose marine batteries (both a starting and deep-cycle). The term “deep cycle” essential means that the battery is meant to be discharged and recharged regularly.

If you look deeper into dual-purpose batteries, there are more sub-categories within it. Those are lithium and lead-acid batteries. Lead-acid batteries include wet cell (flooded), gel cell, and AGM batteries.

The only battery of all of these that needs regular maintenance is wet cell (flooded) lead-acid batteries . When electrolyte levels get low in a wet cell (flooded) battery, you need to refill it with distilled water. If you want to see how to do that, click here .

Gel cell is similar to wet cell but uses a gel that doesn’t evaporate over time, meaning you don’t have to refill it. AGM works similarly to gell cell and wet cell batteries; however, it uses a special glass mat separator instead of liquid or gel.

How to know if your marine battery needs to be replaced

The biggest signs you need to replace your marine battery are if your motor won’t start, your onboard electronics don’t work, there’s visible damage on your battery, or your battery reads below 12.4 volts at a full charge.

Marine batteries experience a rough life as harsh waves constantly bash them around. So make sure to check the battery every once in a while for damages or any loosened connections. Always immediately replace a battery, battery wires, or battery terminals if they are damaged to avoid possible disaster.

If you check your marine battery’s voltage, it should read at 12.6-12.8 volts at a full charge. So if you want to maintain top performance out of your batteries, change them when they read below 12.6 volts. However, they should still work fine between 12.4-12.6 volts; they’re just more susceptible to randomly not working out at sea.

Most boats will give you a warning if your battery voltage is low. However, it’s best to know that before you go out on the water.

How to check the voltage on a marine battery

To check the battery voltage, you need to get a multimeter such as this one on Amazon. You then connect the multimeter’s negative wire to the marine battery’s negative terminal and the positive wire to the positive terminal. Watch this video if you need help:

Why do marine batteries die?

Over time, all batteries eventually die as they cannot be used forever. However, they often die faster than they should due to people not fully understanding them.

According to crownbattery.com , Overcharging, undercharging, fully discharging, sulfation, extreme temperatures, and un-proper seasonal storage are the main reasons batteries die early. These issues can easily be solved as I explain in the next sub-heading.

In summary , this is why marine batteries die early:

• Overcharging
• Undercharging
• Fully discharging
• Extreme temperatures
• Un-proper seasonal storage
• Not cleaning them
• Not doing maintenance on batteries that need it

Another reason boat batteries are dying is dirt. Dirt and debris on the top of your battery and the terminals can become carbonized and drain your battery life. This causes your battery to discharge and recharge more frequently, shortening its lifespan. ( source )

So at the bare minimum, make sure to clean off the top of your battery (including its terminals) with a rag every other week or so. I also recommend using a battery cleaner aerosol such as this one here on Amazon as well.

Tips to extend the life of your marine batteries

As I stated above, batteries die early because of overcharging, undercharging, fully discharging, sulfation, extreme temperatures, and un-proper seasonal storage. Below, I explained how to avoid each of these issues properly.

Additionally, if you have a wet cell (flooded) battery, you will need to maintain it by refilling the cells with distilled water regularly. If you don’t, the battery will have a significantly shorter lifespan. Click here to see how.

1. Don’t overcharge your battery

Although many batteries nowadays have sensors that prevent your battery from overcharging, these fail. Don’t entirely rely on those sensors because overcharging a battery can harm the battery and be dangerous.

Overcharging a battery:

• Increases the risk of a short circuit and an explosion
• Can create unstable conditions inside the battery
• Causes a loss of sulfuric acid and distilled water within the battery
• Heats your battery up and can cause permanent heat damage
• Can cause corrosion on the positive battery plates

Gel cell marine batteries are the most susceptible to overcharging because any lost water cannot be replaced. However, all batteries can be damaged by overcharging, so it’s always recommended never to let it happen.

2. Don’t undercharge your battery

Just like how overcharging your battery is bad, undercharging it could also have damaging effects. So, Always charge your marine battery to full before unplugging the charger.

Not fully charging a battery can cause sulfation which worsens the battery’s performance and shortens its lifespan.

Northeastbattery.com recommends to always fully recharge your battery after use and before storing it. You should also charge your stored battery to full every few weeks as batteries drain power in storage.

3. Don’t fully discharge your battery

Irriversal damage can occur if you discharge your marine battery past 50%, but it probably won’t be detrimental. Just try never to go below 30% because that will definitely damage your battery. This is especially true with lead-acid batteries, including wet cell (flooded), gel cell, and AGM batteries.

People who just use their marine batteries for starting their boat and basic electrical accessories won’t run into this issue until they store their boat for a long period of time. In that case, I recommend charging your battery every 2-3 weeks to full or properly set up a trickle charger such as this one .

Other people who will run into this issue are ones that use trolling motors. Trolling motors drain your batter and because you usually don’t have your gas engine on at the same time, the battery won’t receive any power.

So it’s important to check your battery percentage often if you plan on running a trolling motor for an extended period of time. Try to avoid going any less than 50% charge. I recommend getting one or two extra batteries for a trolling motor, preferably a lithium one (such as this one on Amazon) as they are affected less by extreme discharge.

4. Keep the battery out of extreme temperatures

Extreme temperatures can cause corrosion, water evaporation, and many other problems that reduce your battery’s lifespan.

Anything less than -4°F (-20°C) and over 113°F (45°C) is considered too extreme for marine batteries. However, it would be best if you never stored your battery anywhere below 32°F (0°C) or over 100°F (38°C).

The recommended temperature for storing a marine battery is 59°F (15°C). Any temp plus or minus 20 of that should be fine.

Wet cell (flooded) batteries are the most affected by extreme temperatures as the liquid inside can freeze/evaporate because of temperatures. Gel cell batteries are also greatly affected. AGM and lithium batteries can handle temperature better, but they can still be damaged if the temperature is extreme.

5. Make sure to store your battery properly

During the off-season, it’s important to know how to store your marine battery properly.

The first thing to do is disconnect your battery’s negative cable and charge the battery fully. You’ll also probably want to refill the fluid levels if you have a wet cell (flooded) battery. You’ll then want to charge your battery to full at least once every 2-3 weeks or trickle charge it properly.

And, like what I mentioned above, make sure you store the battery at room temperature.

6. Always maintain a full charge to avoid sulfation

Sulfation is the buildup of lead sulfate crystals inside lead-acid batteries (it doesn’t happen in lithium batteries). This is bad because as the sulfate crystals build up more and more, your battery capacity will shrink smaller and smaller and eventually die.

You usually cannot see sulfation as it happens inside the battery, but if it gets bad, it may look like this around the terminals:

Sulfation is the leading cause of early battery failure in lead-acid batteries. All lead-acid batteries will experience some sulfation, but you can easily limit it by maintaining a full charge.

Not only do you need to keep your battery fully charged to avoid bad sulfation, but you also need to avoid undercharging, extreme temperatures, and extreme discharge. So essentially, just follow all of the other tips to avoid sulfation.

Getting a battery desulfator such as this one on Amazon will reverse some sulfation in your battery and help prevent any future sulfation. I highly recommend getting it to extend the life of your battery.

7. Clean your battery regularly

Dirt and debris on the top of your battery and on its terminals will slowly cause your battery to drain. This could cause your battery to fully discharge or use more charge cycles. Both of which damage your battery.

I mentioned this earlier in the article, but make sure to clean off the top of your battery (including its terminals) with a rag every other week or so. I also recommend using a battery cleaner aerosol such as this one here on Amazon as well.

8. Do proper battery maintenance if your battery needs it

Besides cleaning maintenance, the only battery that needs regular maintenance is wet cell (flooded) batteries. These batteries must be refilled with distilled water every 6-12 months . Here’s a link to Amazon for distilled water if you need to get some.

In order to refill a battery with water, you first need to charge it to full. Then fill each cell up to about 1/4″ from the cell or fill well bottom. Here’s what the process looks like:

If you’re not totally sure what to do, check out this video below:

What type of marine battery is the best?

Undoubtedly, the best overall marine battery is lithium batteries. Not only do they last the longest, but they’re also lighter, more efficient, and don’t require any maintenance. However, they generally cost 2-3 times more than lead-acid batteries.

Out of all the lead-acid batteries, AGM is by far the best. compared to wet cell (flooded) batteries, AGM batteries last longer, hold charges for much longer, and require no maintenance. Also, AGM batteries only cost 1.5-2 percent more than wet cell (flooded) batteries.

Here is how I would list marine battery types:

• Lithium batteries (specifically lithium-iron)
• AGM batteries
• Gel cell batteries
• Wet cell batteries

What marine battery brands are the best?

As for brands, there are many on the market, and it’s hard to choose which is the best. However, there are a few that consistently receive good reviews. These are:

• Dakota Lithium
• Odyssey Battery
• Optima Batteries
• Bass Pro Shops

Just because your battery or the one you’re looking for isn’t from a brand on this list doesn’t mean it’s not good. The best thing you can do is read reviews. There are a lot of bad brands out there, but good reviews will ensure you are getting a quality product.

Other related questions people ask

How often should you charge a marine battery.

You should charge your marine battery to full at least once a month if you are not using it. Although AGM and lithium batteries usually don’t need to be charged for 6+ months. Using a trickle charger is a great way to charge your battery automatically.

How do you properly charge a marine battery?

To charge a marine battery, simply plug in your battery charger and take the negative terminal wire from it and connect it to the negative terminal on the battery. Then take the positive terminal wire and do the same but to the positive terminal. Click here to see a video on it.

Should you leave your boat battery charger on all the time?

No, you should not leave your marine battery on the charger at all times, especially if it’s not a smart or trickle charger. Even smart and trickle chargers can overcharge your battery, so it’s never recommended to leave your batteries charging at all times.

Does a boat battery charge while the engine is running?

Yes, almost all marine engines will charge your batteries while the engine is on. This is done threw an alternator that charges the starting (cranking) battery. Any batteries not connected to the alternator will not charge.

Can you use a trickle charger for marine batteries?

Yes, you can use a trickle charger for marine batteries. They are great because they don’t generate much heat when charging your battery. Some trickle chargers can safely be left charging the battery for months if you set them up correctly.

How do you change a boat battery?

To change a marine battery, you need to first get a pair of latex gloves for safety. Then unscrew the negative terminal, followed by unscrewing the positive terminal. Then take the battery out and replace it with a new one. On the new one, make sure to connect the positive terminal first. This video will help you out.

Should you disconnect your boat battery in the winter?

Yes, you should disconnect your boat batteries in the wintertime. You will want to store them at room temperature and make sure they maintain a full charge by charging them once every month or so. Check out this article I wrote to learn more.

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Born Again Boating

How Long Do Boat Batteries Last? And How to Make Them Last Longer!

Boat batteries can be expensive, knowing how to properly care for them and extend their life can save you a lot of frustration and money! Here’s exactly how…

How Long Do Boat Batteries Last? Most marine batteries last anywhere from 2 to 5 years depending on the level of care you give them. Most batteries come with a one year warranty, but more expensive batteries might come with up to three years of warranty.

This article will teach you how to properly care for marine batteries and how you can make your boat’s battery life last as long as possible!

Why Do Boat Batteries Go Dead?

The single most overlooked factor in keeping your boat’s batteries healthy, running properly, delivering the correct output and living as long as possible is cleanliness.

Did you know: Dirt, dust, salt or any other type of debris. Sitting on top of your battery can cause the battery to drain itself?

It’s true! We can take a battery voltage meter to the battery terminal and notice it reads 12 volts. Then, if we put the red meter lead in the middle of the battery.

(Where there was debris present) the meter will indicate a loss!

You can lose a lot of voltage just across the dirt on the battery. It isn’t just that particular tested spot either. When we checked all over the battery, the constant drain remained.

As batteries age, there are several components that wear out and ultimately get worse. (Even when you clean the top of the battery).

However, by keeping the top of the battery clean, we can ensure there is no wasted drainage. This tip can be implemented immediately. Make sure those battery tops are squeaky clean!

Understanding Boat Batteries

Although we won’t go into the specifics of batteries (AGM’s, flooded, etc).

It is mainly important to know whether your marine battery requires maintenance or is maintenance-free.

Maintenance batteries can be identified by the accessible ports on the top of them.

This is where you can add distilled water to the battery.

Note: you NEVER want to add battery acid to these types of batteries, just distilled water.

Once you pop the top off. You can see whether the battery water level is low or not. You want to maintain the water level up to about a ¼” from the top of the battery.

So that the cap terminals can still stick down into the water level opening. Be sure to use goggles and gloves for safety purposes! Whenever you are filling a battery.

With maintenance-free batteries, on the other hand, none of this is required. Instead, what we have to do is make sure the batteries remain charged up at all times.

The best way to check the charge of your battery is by using a load tester. You can pick up a standard analog load tester at your local auto parts store.

Or you can use this link here for our recommendation of a load tester from Amazon!

What this analog load tester does is put a huge amp draw on the battery. It does this to verify if the battery holds up while under that load or not.

We are looking to make sure that the battery voltage does not drop to less than 10 volts.

9.5 volts is the lowest that most outboards will be able to start with. If it takes to long to turn over, they won’t start with much less than that.

There are more expensive ways of checking a battery though. By using more advanced testers. Although not required, these devices display interesting additional info such as cranking amperage percentages.

This shows you the ability of the battery. How much life it has left and whether you need to charge, retest or replace the battery.

How Often Should You Charge A Boat Battery?

If you want your boat batteries to last longer. Then they will need to get charged! The most common question we receive from clients is “Should I leave my boat battery charger on all the time?”

Our answer is typically a yes and no. Let me explain…

There are many different types of chargers ranging from onboard boat chargers to plain battery chargers. The main thing to remember with any setup is the amperage that we are putting into the battery.

And for how long?

A lot of batteries fail because they’ve been overcharged. This happens when the chargers essentially “cook” the battery until it no longer holds a charge.

This is most common in boats with onboard battery chargers. Although it can also happen if the engine’s charging system fails as well.

If you are going to leave a charger hooked up to a battery for an extended period of time. It is important to use a “trickle charger” or a really low amp charger such as a 2-amp charger.

This will prevent it from cooking the battery. If you leave your battery with a 10, 12, or 15 amp charger. You risk cooking it and causing it to fail a lot sooner than it should.

Additionally, you never want to leave your battery charger hooked up to the batteries and on at all times. The best practice is to use the charger for a day or two. And then leave it unhooked for a week or two.

“Cycling” charges like this can significantly extend the life of your battery and prevent overcharge.

Although most new chargers have sensors built into them that are designed to prevent overcharging once full. These sensors commonly fail after the charger is a few years old so don’t rely too heavily on this.

How Long Does A Marine Battery Hold Charge?

How often do you use your boat? If you are regularly using your boat, the engines will be charging the batteries and there isn’t such a big need to use a battery charger.

Most engine gauges indicate the voltage output of your battery and whether it is charging or not.

You can also check to see if the engine is charging the battery by putting your meter on it while the engine runs.

If you don’t have a voltage meter, you can get one from Amazon from here!

When you do check, you should see somewhere around 14 volts with the engine running. (Sometimes slightly more or less depending on engine RPM’s as well as the age of the engine).

If you advance the throttle just a bit, you should see the voltage steadily climb a little bit towards 14 volts.

To learn all about Outboard Alternators & Outboard Charging Systems , read that article that we wrote about them.

What you DON’T want to see is 15 or 12 volts. This means your engine is either overcharging or not charging at all!

Either of these cases will wear out the battery and shorten its lifespan.

Marine Battery Life

By now we’ve covered cleanliness and other battery information. But it’s also important to break down critical information regarding battery terminals.

When it comes to battery terminals, loose or dirty connections can wear out your battery! Along with parts of the engine starting system due to it not receiving the right amount of amperage.

Think of this scenario like breathing through a straw. Yes, you can do it (for a short period of time that is). But if you do it for too long (and with a small enough straw).

You will eventually pass out! With your engine parts, on the other hand, they will eventually just die out, costing you lots of money.

This is why we recommend using something like a CRC battery terminal protectant to help keep the connections free from dirt and corrosion.

Changing and Maintaining A Boat Battery

A quick tip on changing your boat’s batteries. Whenever you change them, we recommend that you pair all of battery terminal connections with a zip tie.

This way, a ground wire doesn’t get forgotten whenever we put the connections onto the new battery. This will also prevent you from hooking up the terminals backward which can result in serious engine damage!

A lot of clients ask us about colder climates and how it relates to batteries. If you live in a colder climate and have to “winterize” your boat.

You most likely take your batteries out of the boat and store them inside a garage or someplace fairly warm for the season. This is great as it will definitely help extend the life of your batteries.

If you want to take it a step further. The proper thing to do is to hook your batteries up to a “trickle charger.” And keep them out of the cold weather. Once the warm season comes along, you can put them back into the boat.

If you zip-tied all of your wires together as we recommend, the process should be faster and smoother.

For even more information read our in-depth breakdown article about Boat Batteries Freezing & Even Getting Wet.

Fixing A Draining Boat Battery

It happens…

Having a constant drain on a battery of any kind is obviously not a good thing. Fortunately, there are several ways for us to determine if there is a drain on our battery and what is causing it.

Note: You want to be careful in doing this test. Because it can damage your meter if too much amperage is sent through it while performing the following test.

In order to identify what is called a “parasitic draw” on your battery. We first want to switch off the battery and make sure the boat’s key switch is off as well.

Next, disconnect the ground cable from the battery. With the meter set to amps. We will put the positive (+) meter to the ground cable and the negative (-) meter lead to the battery.

This will show us how much amperage is currently being drawn out of the battery.

It is not uncommon to see a few millivolts, however, we don’t want to see anything more than that. If there happens to be a consistent draw showing up on the meter.

We will have to go through the breakers or fuses that feed all of the boat’s components and do some testing.

You will need to pull each fuse out one by one until we see the draw go away.

At this point, we can troubleshoot that specific item in order to stop the parasitic draw from draining out the battery.

Knowing how to operate the battery switch is another technique that can help you prolong your batteries life.

As it gives you complete control of the charging voltage coming from the engine. A lot of new boats have what are called “charging relays” or “ACR’s. These are also referred to as “voltage sensing relays” or VSR’s.

These are isolators that automatically sense which batteries need to be charged and which ones don’t. These sensors automatically combine the batteries when charging and then disconnect them when there is a draw on the batteries.

We can do the same thing by simply using the battery switch. If there is more than one battery in the boat. (We recommend two batteries for any boat bigger than 16 feet with electronics.)

Read this article here if you are unsure about How Many Batteries Should Your Boat Have?

The battery switch will be a 4 position or a combining battery switch. What you do is the following:

Whenever you first start the boat, you can start it using either battery or both. You can even start it twice, checking both batteries one at a time. To make sure they can start the boat individually.

Once the engine is running. Simply turn the switch to the “both” or combined position while being careful not to turn it to the off position while the engine is running.

What this will do is allow the engine to charge both batteries at the same time. While you are running so then when you arrive at your destination. You can turn the engine off and return the battery switch to either one or two.

This way, when you are ready to go and have had your radio, bottom fish finder, live well pumps and washdown pumps draining that battery for the entire time your engine wasn’t running.

You can switch over to the second battery and start the engine!

Then, put it to the combined position again before taking off in order to charge up that drained battery while you’re running back home!

This will help prolong the life of the batteries by maintaining them properly and keeping you from being stranded with a dead battery!

For more information check out our video on this subject!

Check Us Out!

Now that you know how to make your boat batteries last longer. You should check out these other helpful articles packed full of information to help you with your boat!

How To Get More Hours Out Of Your Outboard With Less Break Downs!

Does your boat have the right propeller & how to check.

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Boat Battery Lifespan & How To Extend It [Easy Steps]

A boat battery can last 3 to 5 years , with some even going to 10 years due to their size and with proper maintenance.

If you find your boat battery is dead after one year or the start of a new season, then it’s because you’re not doing proper maintenance on the battery.

Lead-acid batteries, which boats use, go flat and die if they’re not being used. If you’re not driving your boat for more than a month, then you need to do some extra steps to keep your battery going for years.

Extending Your Battery’s Lifespan

When it comes to your boat, and it’s battery, you need to do more than turn the battery switch to off.

The problem is not that there is a small draw of power on the battery, but the fact that your boat sits for too long. Lead-acid batteries will sulfate when not used for months , which is why your battery dies or becomes weak.

To keep your batteries from sulfating you need to keep them active. Keeping a boat battery active can be as simple as riding it at least once a month or keeping the battery charged.

There are two good options when it comes to keeping your boat battery in great shape, a smart battery charger or a low-wattage solar panel charger.

1. Smart Battery Charger

If you have power near where you keep your boat, you can get a smart battery charger.

You want to use a smart battery charger, as it turns on and off as the battery needs it. Some models of smart battery chargers even have a desulfation mode , which can help bring back weak batteries that have been sitting for too long.

You can get a smart battery charger here (ad), this one has dual battery charging capabilities. It’s also ideal to get marine battery chargers, as they’re sealed.

When you’re not going to be using your boat for months, you should keep the battery on charge or at least charge it the night before you plan on riding.

2. Solar Battery Chargers

Another option, and my favorite, is to use a solar battery charger (ad). I like this option because it doesn’t require a wall outlet or power, and is far easier to install and deal with.

The key thing about solar chargers is that you don’t want to exceed 5-watts unless you use a charge controller . Too much wattage and it can overcharge the battery, but a charge controller will stop that.

The goal of using a solar battery charger is not so much to charge the battery, but to keep it active and from sulfating. It’s because of this that the solar panel doesn’t need to be in direct sunlight, just some sun needs to get to it. So the panel can be flat, vertical, crooked or whatever, so long as it’s exposed to the outside and can get some sunlight.

How Often Should You Charge Your Battery?

You should charge your boat battery every 30 days , the night before you go ride at least, to keep it happy.

If you can, what I like to do is keep the solar battery charger hooked up all the time and when I’m done riding for the day I put it over the boat cover and leave. I don’t know when I may ride again, but I do know the battery will be ready the next time I go ride. Since I use a low wattage solar charger on my boat battery it doesn’t drain it and when the sun comes out it keeps it happy. The only negative is that there is a tan line of my solar panel on my boat cover, though hanging the panel on something would fix this.

Reviving Dead Batteries – It’s Possible

Reviving a dead boat battery can be a 50/50 shot.

Bringing back a dead battery really depends on the age of the battery and how long it sat. If it’s under a year old, the chances are good that just putting it on a charger will bring it back.

If the battery is more than 3 years old, it’s often just best to get a new battery. I would try to use a smart battery charger with a desulfator first, as you have nothing to lose.

When the battery is over 5 years old and it’s dead, then just call it and get a new battery. You’ll only be creating new problems by trying to bring back a bad battery.

10 Year Lifespan Is Possible

If you do the proper maintenance and keep the battery charged when it needs it, then it’s possible to get 10 years out of a battery, but it’s a gamble.

Batteries are funny things, you may get 10 years out of one but 2 out of the next one. Sometimes new batteries are bad, and sometimes a battery that seems dead just has corroded terminals.

Boat batteries tend to last longer than jet ski batteries, as they are larger batteries. Larger batteries have larger plates and don’t sulfate as quickly.

You should set your expectations to 3 to 5 years for your boat batteries, but if you get 10 years, then you won and should look into getting a new battery soon.

How Do You Know Your Boat Battery Is Bad?

The only way to know if any lead-acid battery is bad is to load test it.

To load test the battery, you need to use a load tester and NOT a multimeter. The cheapest way to load test a battery is to take it to the local autoparts store and let them do it.

If you don’t want a store to test your battery and want to have the tool yourself, you can get battery load testers here (ad).

You need to measure the amps, not the volts. A bad battery can still read the correct volts, but put a load on it (amps) and it drops off. Generally, if the boat is giving you multiple clicks from the engine , then it’s a weak or bad battery.

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The Basics of Lithium Marine Batteries

• By Randy Vance
• September 18, 2024

Lithium batteries have opened up an entirely new category of electrical power for boats. That is due to their energy density, allowing a lithium battery to pack in as much voltage and amps as a lead-acid battery but at one-third to one-half the weight. They’ve been powering professional anglers’ trolling motors for years and, with an inverter, are increasingly common replacements for gensets. Because lithium batteries can recharge in much less time than lead-acid batteries, a short run of an engine’s alternator integrated with a DC-to-DC charger can quickly bring them to full power.

What Kind of Lithium

Lithium iron phosphate (­LiFePO4) is the chemistry settled upon by most battery-makers. Past ­formulas included cobalt and manganese for lithium-ion batteries. Though powerful, they proved hazardous. Runaway discharges caused fires that were inextinguishable—a poor trait in a boat or anywhere. 

Ground Control to ­Major Tom

Regular power updates from your batteries are essential. Some lithium batteries such as X2Power employ Bluetooth wireless communications to report discharge rate, battery temperature, state of charge and more to smartphone apps, bypassing a gauge, saving space on a tight helm. Others, such as Brunswick’s ReLiOn batteries, offer a battery gauge that reports data to an MFD. 

Wake-Up Call

If a ­LiFePO4 battery runs too low, it might ­require an intervention to wake it up—an electronic slap in the face. A shot of voltage wakes the battery management system, which reconnects the batteries so that it can be recharged. Such devices—basically a voltage-adjustable charger (5 volts to 36 volts)—are available for $25 at Amazon. Alternatively, Norsk and Brunswick’s ReLiOn LiFePO4 batteries have a button that wakes them from snooze. Some batteries optionally offer this feature.

Getting a Charge

Be sure the boat’s charge system is amenable to lithium. Some, such as JL’s Charge, can be set to lithium by the user. Others, such as Dual Pro chargers, have to be converted with a module that can only be factory-installed. So far, we haven’t seen onboard chargers that will “slap” their batteries. And they charge them in a different way than lead-acid batteries get charged. Typically, a charger such as Dual Pro and JL Marine’s Charge systems replenish higher-­voltage lithium trolling motors or house batteries through the cranking battery bank by converting cranking voltage to house voltage, which could be 24, 36 or even 48 volts. 

Read Next: Choosing a Lithium Battery for Your Boat

Long Payback Game

LiFePO4 batteries can be fully discharged and recharged up to 10 times more than lead-acid AGM batteries. So, even though they cost up to one and a half times the priciest AGM battery, they continue to deliver power long after AGMs give out, making them cheaper in the long run, also reducing installation charges. They can provide full power to the last amp (they can be discharged to 10 percent without damage when the battery management system shuts them down). Aboard my Ranger 2510 Bay, 60 amp-hours of 36-volt lithium power gives more fishing time than 100 amp-hours of AGM power of the same voltage. 

Cuts Weight

There are two ways to improve performance in a boat. One is to add more horsepower. The other is to remove weight. Take a bass boat with one lead-acid starting battery and three AGM trolling-motor batteries—the equivalent of two heavyweight boxers in the boat. Lithium batteries can cut that weight from 400 pounds to 150, adding speed and efficiency. 

Balance of Power

Note that a lead-acid battery’s weight might be factored into the center of gravity equation of your boat. If the boat is designed to carry battery weight forward and you install lighter lithium batteries, you might have to shift other gear forward, or choose a new prop, to manage the now lifting and falling bow. If the batteries are on the lateral centerline, the CoG won’t be disturbed. Most center-consoles are so arranged. But bass boats, bowriders and cuddies often don’t have space amidships. It might be wise to run such a boat after removing some of the batteries to get a feel for the lighter load.

LiFePO4 batteries are worth the initial money outlay, and the advantages far outweigh the risks. In a new-boat purchase, a set of LiFePO4 batteries could last 10 years—likely longer than your interest in the boat. On a used boat, changes to the boat’s weight can be mitigated and shouldn’t be cause to avoid this important, useful upgrade.

• More: electric motors , Gear , Marine Batteries , NextMarine , October 2024

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How Long Do Boat Batteries Last? (The Average Lifespan)

Written by J. Harvey / Fact checked by S. Numbers

Have you ever had a boat battery that has lasted for as long as you know? Or did you end up, rather inauspiciously, with one dying out way too soon? The thing is, marine battery lifespan depends on charge cycles, frequency of use, and type, among other factors.

This is why you may get common answers like 3 to 5 years to “How long do boat batteries last?” That’s the average range, but some batteries can last for 7 years and even up to 10+ years due to the factors mentioned above.

Table of Contents

Average Life Expectancy of Every Boat Battery Type

1. three types of boat batteries based on functions:, 2. four types of boat batteries based on chemistry:, factors that affect the lifespan of boat batteries, reasons why marine batteries die and how to avoid it, signs that a boat battery is reaching the end of its lifespan, steps for replacing a boat battery, how to extend the lifespan of boat batteries, frequently asked questions.

You don’t have to overcomplicate things by looking at the expected charging and discharging cycle or what’s the typical application of each battery. Look at the ranges assigned to each type of battery first and foremost instead.

Notice how I stressed the phrase “depending on use”. That’s because this aspect will determine the number of cycles that a typical marine battery will experience as it functions. Of course, you’ll also have to factor in the frequency  of usage, i.e., how often you use the battery per year.

• For example, let’s say, you used the boat battery for a total of 5 months per year; then we can assume that the battery will be subjected to around 50 cycles.

A standard medium-duty battery will last you 200 to 300 cycles. If 50 cycles/year is your consistent frequency of use, with minimal deviations, then it will likely last between 3 and 6 years.

• It’s a different story for boats that hit the water regularly with only a few breaks. You may accumulate 200 or more cycles yearly, so if that’s the case, the deep cycle battery lifespan, assuming it’s the same make, will likely only last you 1 to 2 years.

Here’s a table outlining the number of cycles you can expect based on the battery’s capacity .

This is why, to make your life easier with the longest-lasting battery, opt for a heavy-duty lithium battery.

Or, if you like to only get a starting battery to get the boat’s motors to run, get an AGM battery instead of a standard lead-acid one. This battery type can last much longer, with a 12V one being able to stay in service for 5 to 10 years.

Types of Boat Batteries

Fundamentally, there are three kinds of marine batteries:

• Starting – Starts boat engines using a powerful burst of energy. They need to be recharged by the engine’s alternator and can’t handle continuous use.
• Deep-cycle – These are the opposite of starting batteries in that they discharge slowly and continuously to power up the engine and other components like windlasses, audio systems, fish finders, etc.
• Dual-Purpose – These batteries are versatile enough to function as both starting and deep-cycle batteries. They have become close to permanent presences on boats running on a trolling motor due to this reason.

Boat batteries can be further subdivided based on chemistry:

• AGM (Absorbent Glass Mat) Batteries

Despite being heavier and having a lower capacity than most, these batteries don’t leak and have a lower self-discharge rate. They also require little to no maintenance.

• Flood Lead Acid (FLA) Batteries

These are generally considered old, heavy, and require water to be maintained, but are more economical compared to newer types.

• Gel Batteries

These also don’t spill and are low maintenance, with a lower self-discharge rate than FLA batteries. They’re also hefty, though, and have a relatively low capacity.

• Lithium-ion Batteries

Favored for being long-lasting and fast-charging, li-ion batteries also stand out because of their safety, low maintenance, remote monitoring, and capability to provide consistent output. They are premium choices price-wise, though.

• Type of battery – as the tables above prove, certain types have more longevity, with lithium-ion being supreme powerhouses, as they can work for a decade or two.

This is made even more apparent if we compare them to their lead-acid, deep-cycle counterparts that need to supply power continuously, which may not even last more than two years. 

• Climate and extreme temperatures – climates with regular and drastic temperature shifts may not be too amenable to your battery’s lifespan. The same rings true for humid and rainy locales where corrosion remains a constant risk.
• Usage and charging rate – frequent use and charging of boat batteries often mean a shortened lifespan. However, the opposite is just as bad—we’ll explore this in deeper detail below.
• Maintenance – it’s simple, really: proper marine battery maintenance and storage extends its life. 

• Corrosion – this leads to sulfation that may drain the battery’s life and impair its ability to hold a charge. Try to clean its terminals regularly and apply a corrosion inhibitor afterward. Also, keep the battery dry at all times.
• Infrequent or zero usage – if you leave your boat dormant for months or years, that spells bad news since the battery may self-discharge. You can use a maintenance charger to prevent this from happening.
• Parasitic draw – leaving any boat appliance or compartment that draws electricity on will drain the battery, enough to affect its longevity. Therefore, always unplug all the wires connected to the battery’s terminals when the boat is not in use.
• Overcharging and undercharging – doing either regularly has been proven to cause marine batteries to die earlier than the average lifespan. 

To circumvent the issue, always charge the battery with a suitable charger until it’s full, at which point you should immediately unplug the unit.

You can only maintain a marine battery up to a certain point before it starts showing signs that it’s about to go the way of the dodo. How to tell if a marine battery is bad? Keep your senses sharp for these clues:

• The boat constantly fails to start or takes longer than usual to turn over.

The battery may no longer have enough power to meet the engine’s current needs, particularly when starting it. Don’t underestimate this, as this has led to many stranded boaters.

• Clear physical damage.

Acid built-ups, sulfation, bulges, cracks, corrosion, and heat damage are but some signs that your battery has gone through significant abuse and may be failing.

• Electronics not working as they should.

If you notice lights turning off suddenly and the GPS malfunctioning, these could be signs that the battery can’t handle their respective loads anymore.

• If it’s your first time to replace a boat battery, refer to the manufacturer’s manual first to know what you need and where it’s located.
• Turn the motor off, then access the battery. You may need to remove the seats in certain models. Again, know your boat’s layout first.
• Remove the covers and put on gloves and safety glasses.
• Take out the negative battery cable from its terminal. You may need to unfasten it first. Do the same for the positive battery cable.
• Remove the old battery from the slot. Afterward, fasten the positive battery cable onto the new one.
• Place the new battery in the slot and install the negative battery cable.
• Replace the covers.

• Stay on top of signs of damage and other symptoms above.
• Stop completely discharging the battery. You should recharge the battery whenever it drops below 20%.
• Use the right battery for your needs.
• Use power responsibly. Just by minimizing parasitic draw, you’re already lessening their burden.
• Charge them properly . You can keep them hooked to a maintenance charger, for instance, but be sure you’re using it correctly.
• Rely on other sources of power, such as renewable energy.

How often should boat batteries be charged?

The best answer to this is to just follow the battery’s specific charging instructions.

Typically, every 30 days will do for lead-acid batteries, or you can rely on a maintenance charger. Lithium-ion batteries can do with a three-month charging schedule, but it’s important to not go below 20% before charging.

How long does a marine battery hold a charge?

If it’s dormant, it can hold it up to six months. Continual usage shortens the need for you to recharge it too just days or weeks.

Tips to fix a draining boat battery

Most boaters see this issue once they take the boat out after storing it for a long time. The solution is simple: disconnect all the wire leads off of the battery’s terminals. You can bid adieu to that pesky parasitic draw once you do this.

Can boat batteries be overcharged?

Yes, as explained above, overcharging is a legitimate risk that can result in a reduced boat battery’s life expectancy. In other words, should you charge the battery for too long , it’ll cause irreversible damage.

Unless you’re using a boat that you need to hand crank to start and can do without an alternator or battery aboard, the answer to the question, “how long do boat batteries last?” will always be your concern.

To summarize, it varies a lot, but how you use the battery and maintain it, relative to its type and capacity, should give you a clearer answer.

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The Complete Guide to Maintaining Your Deep Cycle Marine Battery

Regular maintenance is key to ensuring the longevity and optimal performance of your deep cycle marine battery. In this guide, we'll explore the essential steps to maintaining your battery and ensuring it serves you well for the long haul.

Understanding Deep Cycle Marine Batteries

Before reviewing maintenance, it's important to understand deep cycle marine batteries. Unlike starter batteries, which are designed for short bursts of high energy, deep cycle batteries provide a more sustained power output over an extended period. They're the lifeline of your boat, camper, or off-grid setup, powering everything from lights to appliances.

Regular Inspection and Cleaning

Visual Inspection Matters

Regular visual inspections are the first line of defense in battery maintenance. Check for any signs of corrosion, loose connections, or physical damage. Addressing these issues promptly can prevent more significant problems down the line.

Clean Connections for Optimal Performance

Clean and secure connections are crucial for the efficiency of your deep cycle marine battery. Use a mixture of baking soda and water to clean terminals and cable connections, ensuring a solid electrical connection.

Charging Best Practices

Charge Smart, Charge Right

Proper charging is paramount for extending the life of your deep cycle battery. Avoid deep discharges, as they can significantly impact battery health. Invest in a quality marine battery charger and follow the manufacturer's recommendations for charging cycles.

Avoid Overcharging

Overcharging is a common culprit behind premature battery failure. Invest in a charger with an automatic shutoff feature to prevent overcharging. This ensures your battery is always ready without risking damage.

Storage Tips

Prepare for Storage

When preparing for extended storage, taking the necessary steps to preserve your deep cycle marine battery is crucial. Begin by fully charging the battery before storage. A fully charged battery is better equipped to withstand the natural self-discharge that occurs over time.

Disconnect to Prevent Parasitic Drains

To further protect your battery during storage, disconnect it from any devices or systems that may cause drains. Even when not in use, some electrical components draw small amounts of power. This can lead to a partially or fully discharged battery when you return.

Ideal Storage Conditions

The right storage conditions are vital for maintaining your deep cycle marine battery's performance and lifespan. Store the battery in a cool, dry place, away from direct sunlight and extreme temperatures. Exposure to heat or cold can affect the chemical reactions within the battery, impacting its overall health.

Consider Using a Battery Maintainer

For added protection during storage, consider using a battery maintainer or trickle charger. These devices provide a low, steady charge, preventing the battery from discharging excessively. This also ensures it stays in optimal condition. Battery maintainers are especially useful for long-term storage periods, such as during the winter months.

Deep Cycle Battery Discharge

Monitor Discharge Levels

Regularly monitoring the depth of discharge (DoD) of your deep cycle marine battery is crucial for its overall health. Avoid allowing the battery to discharge below the recommended levels because this can lead to irreversible damage.

Equalization Charging

Periodic equalization charging is important to prevent the accumulation of sulfation. Sulfation occurs when lead sulfate crystals accumulate on the battery plates, reducing its capacity and performance. Equalization charging helps break down these crystals, ensuring the battery operates at its best.

• How often should I visually inspect my deep cycle marine battery?
• Aim for monthly visual inspections, especially during heavy usage periods.  Follow your battery manufacturers recommendations. 
• Can I overcharge my deep cycle battery if I leave it connected to the charger for an extended period?
• Yes, overcharging can damage your battery. Invest in a charger with an automatic shutoff feature or have a battery with an internal BMS with overcharge protection.  Follow your battery manufacturers recommendations. 
• What is equalization charging, and how often should I perform it?
• Equalization charging balances the cells in your battery. It's recommended every 3-6 months, depending on usage. Follow your battery manufacturers recommendations. 
• Is it necessary to disconnect my battery during storage?
• This depends on the application and setup but disconnecting prevents parasitic drains and ensures your battery is ready for use when you return.
• Can extreme temperatures affect my deep cycle marine battery?
• Yes, store your battery in a cool, dry place to maintain optimal performance.

Follow these guidelines and your deep cycle marine battery will continue to be a reliable power source for all your adventures. Regular maintenance ensures that you get the most out of your investment, keeping you powered up wherever your journey takes you. This article is part of an ongoing series about Marine Deep Cycle batteries . Check out our other article " Unlock the Power of Deep Cycle Marine Battery: 11 Tips for the Perfect Boating Adventure "

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Marine Battery Essentials: What You Need to Know

The marine battery is an essential component of any boat’s electrical system, providing power to a variety of items including navigation equipment, lighting, and engine starting. It’s crucial to understand the basics of marine battery selection, installation, and maintenance to ensure reliable, safe, and efficient operation of your boat’s electrical systems. This article will guide you through marine battery essentials and address what you need to know.

Types of Marine Batteries

There are three main types of marine batteries: starting batteries, deep-cycle batteries, and dual-purpose batteries.

Starting Batteries

These batteries are designed to deliver a high burst of current to start the boat’s engine. They have a large number of thin lead plates that enable them to discharge high currents quickly. However, they are not suitable for powering electrical devices for extended periods.

Deep-Cycle Batteries

Deep-cycle batteries are designed to provide a steady amount of current over a long duration. They have thicker lead plates, allowing them to be discharged and recharged repeatedly without causing damage. Deep-cycle batteries are ideal for powering electrical devices like trolling motors, equipment, and appliances on board.

Dual-Purpose Batteries

As the name suggests, dual-purpose batteries combine the functions of starting and deep-cycle batteries. They can provide the high current needed for engine starting while also supplying power for electrical devices on board. Although they may not perform as well as dedicated starting or deep-cycle batteries, they offer a convenient, all-in-one solution for boaters with limited battery storage space.

Marine Battery Size and Capacity

Marine batteries come in various sizes and capacities to accommodate different types of boats and electrical load requirements.

Battery Group Size

The battery group size is a standardized classification system that indicates the physical dimensions of the battery. Common marine battery group sizes include 24, 27, and 31. The appropriate group size will depend on your boat’s battery compartment size and the specific battery manufacturer’s recommendations.

Ampere-Hour (Ah) Rating

The capacity of a marine battery is measured in ampere-hours (Ah), which signifies the amount of current the battery can supply for an hour before being completely discharged. A higher Ah rating indicates a larger battery capacity, which can power more electrical devices or last longer under the same load. When choosing a marine battery, it’s essential to consider your boat’s electrical demand and select a battery with adequate capacity to supply the required power.

Battery Maintenance and Safety

Proper maintenance and safety precautions are necessary to ensure optimum battery performance, extend service life, and avoid potential hazards.

Periodic Inspection and Cleaning

Regularly inspect your marine battery for any signs of damage, leakage, or corrosion around the terminals. Keep the battery clean by wiping it down with a damp cloth and removing any dirt or deposits on the terminals. To prevent corrosion, it’s recommended to apply a thin layer of dielectric grease or petroleum jelly to the terminals after cleaning.

Charging and Maintaining Proper Water Levels

Regularly charging your battery will help it last longer and perform better. Use a quality marine battery charger designed for your specific type of battery to ensure safe and efficient charging. If you have a flooded lead-acid battery, it’s essential to maintain the proper electrolyte levels by adding distilled water as needed. Be sure to follow the manufacturer’s specific instructions regarding charging and electrolyte maintenance.

Safe Battery Storage and Ventilation

Make sure to store your marine battery securely in a well-ventilated battery box or compartment on your boat. This will protect the battery from physical damage, moisture, and excessive heat, which can all contribute to decreased battery performance and service life.

Follow Manufacturer’s Recommendations

Always refer to your marine battery manufacturer’s recommendations for installation, charging, maintenance, and safety precautions. Adhering to these guidelines will ensure maximum battery performance, longevity, and safety on board.

Understanding the essentials of marine batteries is crucial for any boat owner. By selecting the right type and size of battery, ensuring proper installation and maintenance, and prioritizing safety, you can optimize the performance and lifespan of your marine battery, providing your boat with reliable power for all of your on-the-water adventures.

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Why Does My Boat Battery Keep Dying? (Boating Batteries Explained)

Experiencing a dying boat battery can be both frustrating and perplexing, especially when it happens repeatedly. There are various reasons why your boat battery might keep dying, and understanding these causes is the first step in solving the issue and ensuring smooth sailing.

The most common reason a boat battery keeps dying is due to its age. Over time, boat batteries lose their ability to hold a charge and may need to be replaced. Another possible issue leading to battery failure is a charging problem with the engine, often stemming from a malfunctioning rectifier. Lastly, a parasitic draw could be draining the battery even when it’s turned off.

By considering these potential causes of battery failure, you can better diagnose the issue and take appropriate action to resolve it.

Table of Contents

Boat Battery Died: Common Reasons

Age and Maintenance

One crucial factor that affects your boat battery’s life is its age and maintenance. A dead battery often results from a lack of routine maintenance, which includes checking the electrolyte levels and charging the battery properly.

A marine battery typically lasts for 3-5 years, depending on its usage and care. Keep up with your battery’s maintenance schedule and consider replacing it once it reaches its expected lifespan.

Parasitic Draw From Bilge Pump or Other Devices

Parasitic draw occurs when electrical devices continue to consume power even when the boat is not in use. Some devices, like a bilge pump or CO detector, must run at all times to ensure your boat’s safety.

However, other devices, such as radios or GPS systems, should be shut off when the boat is not in use to prevent unnecessary battery drain. To identify a parasitic draw, use a digital multimeter to measure current flow from the boat’s electrical system .

Sulfation (Lead Acid Batteries)

Sulfation is a chemical process that occurs in lead-acid batteries when lead sulfate crystals build upon the battery plates. If a battery remains in a discharged state, the lead sulfate will harden, reducing the capacity to hold a charge.

Regular charging and usage of your boat battery can prevent sulfation, but if it occurs, you may need to replace the battery .

Corrosion and Wiring Issues

Corrosion affects boat batteries because of exposure to moisture and saltwater. Check regularly for signs of corrosion on the battery terminals, and clean them using a wire brush and a baking soda solution to maintain proper electrical connectivity.

Inspect the wiring and cables leading from the battery to the engine and other electrical systems. Loose, damaged, or corroded connections can cause energy loss and prevent the battery from being charged.

Check for blown fuses and replace them if needed. To prevent further issues, ensure proper battery cable connections between the positive cable and the battery’s positive terminal, and between the negative cable and the battery’s negative terminal.

Remember, maintaining your boat battery, addressing parasitic draws, preventing sulfation, and addressing corrosion and wiring issues will mitigate the risk of a dead boat battery. Regular inspection and proper charging will help prolong your marine battery’s life and keep your boat ready for the water.

Types of Boat Batteries and Their Roles

There are various boat battery types to fit your boat’s different needs. Understanding the difference between them helps you choose the right one for your usage. This section will cover three types of boat batteries: Starting Batteries, Deep Cycle Batteries, and Dual-Purpose Batteries.

Starting Batteries

Starting batteries are designed to provide a quick and powerful burst of energy to start your boat’s engine. They have more, thinner lead plates which enables them to deliver higher current in a short time. However, they are not meant for long-term discharge, as they can lose their ability to hold a charge if drained continuously.

Highlights:

• Provides quick and powerful energy
• Designed for starting engines
• Not meant for long-term discharge

Deep Cycle Batteries

Deep cycle batteries are designed to provide a steady current over a longer period. They have fewer, thicker lead plates, making them more suitable for continuous discharge. These batteries are commonly used to power accessories such as lights, electronics, or trolling motors.

Although deep cycle batteries can start an engine in a pinch, it is generally not recommended due to their specialization in providing steady power.

• Provides steady current over a longer period
• Designed for continuous discharge
• Ideal for powering accessories

Dual-Purpose Batteries

Dual-purpose batteries attempt to offer the best of both worlds, combining the high current capability of starting batteries with the continuous discharge characteristics of deep cycle batteries. Although they serve the roles of both types reasonably well, they may not perform as optimally as dedicated starting or deep cycle batteries in specific situations.

• Combines characteristics of starting and deep cycle batteries
• Versatile, serving both roles
• May not perform as optimally as dedicated batteries in specific applications

Remember, it is essential to choose the right type of boat battery for your needs, consider the roles you need it to perform, and maintain it properly to ensure its longevity.

Battery Charging and Monitoring For Boating

Your boat’s alternator is responsible for charging the battery while the engine is running. A faulty alternator can result in a poor charge or a complete failure to charge your battery. Be sure to regularly inspect and maintain your alternator to prevent battery-related issues.

Battery Charger

A battery charger is an essential tool for maintaining your boat’s battery health. Opt for a smart marine battery charger with a three-stage charging process:

• Bulk stage: The charger provides a constant current to the battery until it reaches about 80% of its capacity.
• Absorption stage: The charger gradually reduces the current and maintains a constant voltage to avoid overcharging.
• Float stage: The charger maintains the battery at full charge without overcharging it.

A marine battery charger like the ProMariner Waterproof Marine Battery Charger (Amazon) will do the trick. Not only will it protect your battery as it’s charging, it will charge your battery fairly quickly if it has been drained.

Using a cheap automotive charger may lead to shortened battery life in the long run.

Trickle Charger

A trickle charger is a low-current charger designed to maintain the charge level of your boat’s battery during periods of inactivity. It supplies a small, consistent amount of current, preventing the battery from discharging or becoming damaged due to long-term disuse.

They are typically connected to an AC power source and convert the power to DC for charging the battery.

The Foval Automatic Trickle Battery Charger 12V at Amazon is an example of a low-cost quality option for trickle charging batteries.

Switches and Fuses

Switches and fuses play a crucial role in protecting your boat’s battery from short circuits and overloads. When you’re not using your boat, be sure to isolate the batteries with a quality battery switch to prevent any potential parasitic draw.

Fuses should be present in the circuitry connecting various electrical components to the battery. Regularly inspect and, if needed, replace damaged or corroded fuses to ensure proper battery function.

In conclusion, for optimal boat battery performance, you should regularly monitor and maintain your charging system, including the alternator, battery charger, trickle charger, switches, and fuses. This will help prevent your boat battery from dying frequently and ensure a longer battery life.

On-Board Electronic Devices and Their Impact on Batteries

Trolling motor.

Trolling motors can have a significant impact on your boat’s battery life. They require a steady supply of power to operate effectively. As you use your trolling motor, it’s essential to monitor your battery voltage and ensure that it stays within the recommended range.

If your trolling motor constantly drains your battery, consider investing in a separate, dedicated battery for it. This will help balance the power load between your various on-board devices.

Fish Finder

Fish finders are another electronic device that can drain your boat battery. Most fish finders use relatively little power, but they can still contribute to battery drain if left running for long periods.

To minimize battery drain from your fish finder, turn it off when not actively in use and check for any appropriate power-saving settings within the device. Additionally, regularly reviewing device’s battery usage can help identify any potential issues early on.

Radio and Other Entertainment Devices

Boat radios, CB radios, CD players, and other entertainment devices are also potential sources of battery drain. Leaving these devices on or in standby mode when not in use can lead to power being consumed, even if they are not actively being used.

Be sure to turn them off completely when not needed. Consider using portable, battery-powered options for these devices, as they won’t draw power from your boat’s primary battery.

Navigational Instruments and Gauges

Navigational instruments, such as GPS devices, and gauges for monitoring boat performance also rely on your boat’s battery. While these devices typically have lower power consumption, they can still contribute to battery drain if not managed properly. To extend battery life, be mindful of the following:

• Turn off navigational devices when not in use
• Regularly calibrate and maintain your gauges to ensure accurate readings
• Consider installing a battery monitor to track battery usage and identify potential issues

By taking the time to manage your on-board electronic devices, you can help prevent unnecessary battery drain and extend the life of your boat battery.

Troubleshooting and Reviving a Dead Boat Battery

Jump-starting (safety).

If your boat battery is dead, one of the quickest solutions is to jump-start it. To do this, you will need a spare battery or another boat’s battery. Follow these steps:

• Turn off all electrical equipment on your boat.
• Connect the positive (+) terminal of the dead battery to the positive (+) terminal of the good battery using jumper cables.
• Connect the negative (-) terminal of the good battery to the negative (-) terminal of the dead battery using another jumper cable.
• Start the boat with the good battery, and then start the boat with the dead battery.
• Disconnect the jumper cables in the reverse order in which they were connected.

Always exercise caution and follow safety guidelines when jump-starting batteries.

Battery Load Testing

A battery load tester can help determine your battery’s health. Follow these steps to test your battery:

• Turn off all electrical equipment and disconnect the battery cables.
• Connect the battery load tester to the battery terminals according to the instructions provided.
• Perform a load test, and check the voltage reading. See the following table for the ideal voltage readings:

If the battery’s voltage is within the dead battery range, consider replacing it. If the voltage is low but not dead, recharge the battery and retest.

Replacing the Battery

If your battery is consistently dying or tests show it’s no longer able to hold a charge, it’s time to replace it. Here’s how:

• Purchase a new battery that is compatible with your boat’s specifications.
• Disconnect the negative (-) cable from the dead battery first, followed by the positive (+) cable.
• Remove the dead battery and securely install the new battery in its place.
• Reconnect the battery cables, connecting the positive (+) terminal first, followed by the negative (-) terminal.

Regularly maintain your new battery by monitoring its state of charge, checking for corrosion, and ensuring it’s properly charged to prolong its life.

Boat Battery Care and Longevity Tips

Regular maintenance.

To ensure your boat battery lasts as long as possible, it’s crucial to perform regular maintenance. Inspect the battery terminals and remove any corrosion using a wire brush. To prevent further corrosion, apply a thin layer of dielectric grease to the terminals.

Check the electrolyte levels in your battery monthly, especially during the boating season. If the levels are low, top them off with distilled water, but never overfill. Overfilling can cause the battery to lose electrolytes and generate excessive heat, ultimately shortening its lifespan.

Follow the manufacturer’s recommendations for charging and testing your battery, and make sure to use a marine-specific, three-stage charger, as these provide a more sophisticated charging regime than cheaper alternatives. Your battery should be fully charged and tested at least once a season.

Proper Storage

Proper storage is essential for battery longevity when your boat sits unused. Store your battery in a cool and dry environment away from direct sunlight, heat sources, or flammable materials. Ensure the battery is stored off the ground on a shelf or platform to prevent it from discharging through the floor.

When storing the battery, disconnect it from the boat’s electrical system to avoid any potential parasitic drains. This also helps meet the requirements of the Coast Guard – disconnecting the battery while the boat is not in use can help deter issues like fires or battery failure.

Winterization

As the boating season ends, you should also prepare your battery for winter storage. Fully charge the battery before storage, and use a trickle charger or a smart charger with a maintenance mode to maintain the charge over the winter months.

It’s essential to protect your battery from extreme cold, as freezing temperatures can affect a battery’s performance and lifespan.

Keep your battery in a well-ventilated area and ensure the electrolyte levels are adequate before winter storage. Monitoring its state of charge and maintaining proper electrolyte levels throughout the winter months will help ensure your battery is ready to go when the next boating season begins.

By following these tips on regular maintenance, proper storage, and winterization, you can help extend the life of your boat battery and avoid potential issues with battery failure, ensuring a smooth and enjoyable boating experience.

Preparing for Emergencies in Case of Battery Failure

In the event your boat battery dies while you’re out on the open water, having an emergency plan and the appropriate gear is crucial. Here are some items that you should have on board and know how to use in case of a battery failure.

Emergency Whistle

An emergency whistle is an essential signaling tool to have on hand. It can help you:

• Grab the attention of nearby boats
• Alert rescuers to your location if you’re in distress
• Signal for help in situations where visual communication is difficult

Keep the whistle readily available, and ensure everyone on board knows how to use it.

Don’t forget to have oars on your boat. When your battery fails, oars can be a reliable and effective means of propelling your boat, especially in situations where:

• Wind or current aren’t favorable
• Your boat engine isn’t functional
• You need to reach the shore or another boat for assistance

Ensure your boat has a suitable set of oars and that you’re familiar with how to use them efficiently.

A flare gun is another critical component of your emergency gear. It allows you to send a visual signal for help, both during daytime and in darker conditions. Having a flare gun available is essential, especially if you’re in a:

• Remote location
• Busy waterway with limited visibility
• Situation where your boat’s lights or other signaling devices aren’t operational due to battery failure

Be sure to understand how to operate a flare gun safely and store it in a readily accessible location on your boat.

As an added measure of protection when out boating, we always carry a small jump starter battery like the NOCO Boost Plus Lithium Jump Starter Box (Amazon) just in case we accidentally run our boat battery down too far to start the outboard. It adds greatly to my piece of mind.

Understanding Boat Battery Warranties

When purchasing a boat battery, it’s essential to be aware of the warranty that comes with it. A warranty can provide you with peace of mind and protection in case you encounter issues with your battery.

Manufacturers usually offer warranties for their boat batteries, typically ranging from one to three years. The warranty period depends on the battery type and the manufacturer’s policy. Make sure to read the warranty terms and conditions carefully to understand the coverage offered.

• Battery coverage : The warranty should specify the types of issues that are covered, such as manufacturing defects or poor workmanship. It may also cover the battery’s capacity or performance, ensuring that it meets the manufacturer’s specifications.
• Exclusions : It is crucial to understand what is not covered by the warranty. Some common exclusions may include damage caused by improper installation, mishandling, or external factors such as accidents or environmental damage.
• Claim process : Familiarize yourself with the process of making a warranty claim. This could involve contacting the manufacturer or the retailer from whom you bought the battery. Ensure you have the necessary documents like proof of purchase, warranty certificate, or any other relevant paperwork.

It’s essential to follow proper battery maintenance procedures to avoid voiding your warranty. Failure to maintain your battery might lead to premature failure or reduced performance, which may not be covered by the warranty. Some preventive measures include:

• Regularly checking and topping up the water levels in the battery.
• Keeping the battery terminals clean and free of corrosion.
• Ensuring your battery is adequately charged before use.

In conclusion, understanding your boat battery’s warranty can save you time and money when dealing with battery issues. So, always read the warranty terms and conditions and ensure you maintain your battery accordingly.

Bryan is a Las Vegas resident who loves spending his free time out on the water. Boating on Lake Mohave or Lake Havasu is his favorite way to unwind and escape the hustle and bustle of the city. More about Bryan.

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Monitoring Your Marine Battery Bank

Two long-time players in energy systems charge to the top spots..

Two recent tests graphically demonstrated the importance of monitoring state of charge in a boats batteries: Tracking Batteries , in the May 2015 issue and AGM Battery Test Update , in the August 2015 issue. These tests demonstrated that a sealed batterys capacity will be reduced over time, if its never brought back up to a full state of charge. But just how accurate are the monitors we use to gauge our batteries states of charge?

It has been 16 years since Practical Sailor looked at battery monitors, so we thought it was high time to take a look at the latest offerings in this area. Certainly, for many cruising sailors, battery banks are among their most important onboard resources, and knowing when you might be running low on electrical fuel is as important as keeping track of potable water and diesel fuel.

Photos by Ed Sherman

The need for accurate monitoring is especially important when you consider that over the last decade, we have seen some important improvements in battery technology as well as other areas of onboard electrical systems. For example, LED lighting systems have finally evolved so that they not only use very few amps to provide high-quality interior light, but they also actually meet international standards, as is the case with running lights. The net result is systems that dramatically reduce the amount of power we need to keep things illuminated.

On the other hand, many cruisers now expect to have such amenities as air-conditioning and refrigeration on board-features once considered luxuries-which has increased their appetite for amps significantly, in spite of product vendors considerable efforts to design in lower power consumption. The bottom line here is that keeping track of your batteries states of charge is especially important for maximizing battery-cycle life. Many boat owners today can easily have several thousand dollars invested in batteries by keeping close track of their batteries state of charge.

What We Tested

For this report, Practical Sailor studied and compared monitoring systems from five different suppliers: Blue Sea Systems, CruzPro, Scad Technologies, Victron Energy, and Xantrex . Among these vendors, we looked at offerings ranging from a simple, red warning-light voltage monitor (Scad) that automatically shuts down heavy electrical loads before a dead battery occurs or turns on a generator to get a battery charger up and running when needed, to very sophisticated adjustment and profile settings (Victron) that can work well with lithium iron phosphate (LiFePO4) battery technologies. Of our test units, the Victron monitors were the only ones to even mention lithium iron technology and make a recommendation for adjusting the units profiling to fit lithium technology and discharge/recharge regimens. It appears that the other vendors really have not tested their products with that battery chemistry in mind.

Its important for readers to understand the limitations of any battery monitoring system. These devices are quite good at monitoring amperage and voltage and keeping track of these values down to 0.1 volts in either case. But when it comes to determining state of charge or hours of use remaining, there are many factors that can introduce some margin of error. This is something our testers had to take into account as well when they established a protocol. (See accompanying How We Tested on right for details on the testing.)

Battery chemistry and internal construction, age, temperature, and rate of discharge and recharge efficiency all play into the degree of accuracy we can expect from a battery monitor. Several of the vendors in our group have given these matters considerable attention and make recommendations to periodically synchronize or calibrate the monitor with the batteries being monitored. Victron, for example, offers an optional temperature sender to provide that data input to their monitors. Some of the vendors did not offer any guidance for calibration, presumably because calibration is limited, if at all possible.

Why does temperature matter? Monitoring battery temperature and building that data into a micro-processor that is sending out a voltage reading is useful for those seeking extreme accuracy. There is a direct correlation between temperature, current (amperage), and voltage. As batteries heat and cool due to both ambient temperature variations and electro-chemical reactions in each cell of the battery, their internal electrical resistances also vary. We know from Ohms Law that as resistance changes (mathematically) both voltage and current will change. In the case of battery monitors that essentially present a voltage reading, monitoring temperature in real time can more accurately depict voltage, and therefore, state of charge.

Why is calibration so important? As your batteries age, a re-adjustment of the charging parameters is really quite necessary in order to maximize the accuracy of your monitor.

When selecting a monitoring system for your batteries, you may need to consider how many battery banks the system can effectively monitor. The Value Guide that accompanies this article will help with these decisions. The CruzPro VAH 110 can provide data for three separate banks of batteries, with its focus being the house bank. The Xantrex unit we tested can only handle two banks.

It is also important to understand that in most cases, the house bank is your primary concern, so complete, comprehensive analysis is provided for the house banks, but the monitoring of auxiliary banks (as the installation instructions will typically describe the secondary banks) will be more limited.

Blue Sea Systems M2

The Blue Sea Systems M2 was the only monitor in our group that utilizes an extremely bright OLED (organic light emitting diode) display. This makes the display easily visible under just about all lighting conditions. The monitor includes an integrated relay that can turn loads on or off, based on the state of charge of the batteries and features a summary screen that displays pertinent information in a single screen.

Of all the units in our test field, the Blue Sea Systems installation guide was probably the simplest to follow. The M2 can work with a battery bank that has up to 5,000 amp hours of capacity and will work with 12-, 24-, 36-, or 48-volt systems. The instructions identified all of the currently available battery types as being compatible; however, they did not mention anything about LION technology.

Bottom line: We liked the ease of use and the visibility of the M2, but the instructions describe only initial setup and made no mention of any synchronization or periodic calibration requirements, so we have questions about its long-term accuracy as the batteries its connected to age.

CruzPro sent us three different units to check out, we tested two of the three: the VAH 65 and VAH 110. We did not test the VAH 60, which is very similar to the VAH 65 unit; the essential difference is the amount of amperage each can handle. These units are limited in their voltage-handling capabilities to either 12- or 24-volt nominal systems and in battery-bank capacity up to 3,000 amp hours. The units offer NMEA 0183 interface capability, which allows you to monitor battery voltage remotely through your multi-function display (MFD) or remote display. They also have a programmable voltage alarm to alert the owner when voltage is too high or too low. Additionally, these units can be calibrated to automatically turn a battery charger on and off at user-selected points.

All of the CruzPro units offer a wide range of adjustability for altering Peukerts Exponent, the fundamental algorithm used by all of our test subjects. The problem is that the methodology involves a great deal of trial and error. The default exponent used for calculating is set at 1.25. This seemed to work well for the flooded-cell, deep-cycle battery we used during our tests, but this exponent is not the same for different battery types, and it will change as the batteries age.

The CruzPro units also offer adjustments for what they refer to as amp-hour drift. CruzPro describes this drift as what happens over extended periods of time when the boat is not in use. During this period, small calibration and measurement errors accumulate and cause the meters amp-hour value to drift away from the actual amp hours available. Again, the method to deal with this is trial and error.

Instructions are provided in the owners manual, but they are a bit subjective (not to mention complicated), in our view. Certainly, some fiddling with the calibration will probably bring the monitor closer to its ultimate accuracy, but just remember that it will likely need readjustment as the battery ages. Our guess is that most people wont bother with these tweaks as they go along, and frankly, the documentation that comes with the product is just too vague to really be helpful. CruzPro explained that the user manuals are short and to the point, because they have found that people tend to not actually read longer, more detailed manuals.

Bottom line: While a techie might get many hours of pleasure tinkering with the CruzPros functions, in our opinion, this line of meters is more complicated than it needs to be for the average boater. Its complicated enough that we would recommend a professional installation in most cases.

• Scad Technologies

The Scad Technologies monitor we tested is basically a simple voltage alert system. It works only with 12-volt systems. The unit offers both an audible and visual alarm and is programmable for both high- and low-voltage values. Additionally, the unit can be wired to shut off a high-current load, such as a DC refrigerator, 30 seconds after the visual alert or 15 seconds after the audible alert is activated. It can also be wired to turn on a generator when the low-voltage alarm gets triggered.

Bottom line: Essentially, this is an inexpensive backup monitor, or an energy-saving switch to preserve battery state.

• Victron Energy

Victron sent us two similar units, the BMV 700 and the BMV 702, which adds features like battery temperature monitoring, basic monitoring of an auxiliary battery, and monitoring of mid-point voltage on larger battery banks.

The comprehensive owners manual does a good job explaining the monitors limitations and the variability in battery monitoring systems in general. It also discusses the Victron monitors programmable functions that help to ensure a higher degree of accuracy. Programmable functions include battery capacity, charged voltage, tail current (a percentage of the battery capacity), charged detection time, Peukerts exponent, charge efficiency factor, current threshold, time-to-go averaging period, zero current calibration, and a synchronization function. All of these functions are explained in great detail in the owners manual with help provided in making initial decisions based on the battery technology in use.

These units have the highest capacity of all the units we tested except the Xantrex LinkPro and can be used to monitor a battery bank with up to 9,999 amp hours of capacity. They can work with 12-, 24-, or 48-volt systems. The BMV units also store history data, which can be used later to evaluate usage patterns and battery health, as well as help in tweaking as the batteries age.

In all, we liked the documentation provided with the Victron energy units over all of the other products in our test group. The fact that the units come with a CAT 5 cable to connect the gauge to the shunt helps to significantly reduce the chance of making a potentially damaging error during installation. Basically, all of the wiring needed to install the unit that is not a part of the boat is provided with the kit.

Finally, the Victron monitors were the only units in our test group to provide information on using them with LION batteries.

Bottom line: The Victron BMV monitors earned the Best Choice pick. They will hold particular appeal to owners with high-capacity battery banks who are leaning toward Lithium Ion. If youre a savvy do-it-yourselfer, the BMVs lend themselves to DIY installation.

The Xantrex LinkPro we tested is quite feature-rich. The voltage limits are for 12- and 24-volt systems only, which cover most applications. Its amp-hour range goes to 9,999 like the Victron units, so connecting to large battery banks will not be an issue. The unit can be equipped with an optional temperature sensor like the Victron BMV 702 model, which we would always recommend as one more data point to improve overall accuracy.

Also like the Victron units, the LinkPro provides a history menu, which testers really liked. The data it provides can help boat owners analyze their on-board electrical habits, both good and bad. A unique feature with this model is the ability to auto-synchronize with the connected batteries. This synchronization function helps to eliminate the need for tweaking adjustments as the battery ages and will go a long way toward ensuring that battery maximum cycle life is achieved.

Bottom line: Also a Best Choice pick, the LinkPro is one of the most popular battery monitors on the market for good reason. The synchronization feature is especially helpful for the non-techie.

After spending a month working with these units and really digging into all of their features and setup requirements, we came up with two winners: the Victron Energy BMV monitors and the Xantrex LinkPro monitor. These monitors offer the highest level of sophistication available today, and we feel they will do the best job in ensuring that you can maximize your onboard battery investment.

For further tips on installing a battery monitor, Practical Sailor contributor Rod Collins of Compass Marine, who carried out the PSs 2015 battery tests , has an illustrated guide on his website .

The degree of accuracy we can expect from a battery monitor depends on a number of factors: battery type, age, rate of discharge, and recharge efficiency, to name a few.

Several of the vendors in our test group recommend that you carry out periodic calibration in order to ensure that the readings are accurate. Victron’s monitors, for example, can be programmed for a range of scenarios. Other makers offer very little guidance on calibration.

1. The Victron units were the most compact and will require very little behind-panel depth for installation. 2. The Xantrex LinkPro offers a temperature monitor sensor option, which we feel is an important addition to enhance accuracy of readings over time. 3. The CruzPro display is large, and the data is in large font. This will make it quite useful for those needing to check the screen from a distance. 4. The Blue Sea Systems LED display will be crystal clear even in the brightest sunlight. In terms of display, it was very well suited for being mounted in the cockpit. 5. The Victron shunt was the only one in our group that supplied a CAT 5 cable to connect the really fine-gauge wires linking the shunt to the instrument display. This simplified installation considerably.

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Marine Batteries: Types, Charging, Wiring & Set Up

Marine batteries are designed specifically for use on a boat, with heavier plates and robust construction designed to withstand the vibration and pounding that can occur onboard any powerboat. For this reason, marine batteries are usually more expensive than automobile batteries, which can tempt some boat owners to purchase an auto battery instead of a marine battery. Don’t make that poor decision. A marine battery will last longer and be more reliable than an auto battery in a boat.

Boat Maintenance Guide

Types of Marine Batteries

There are three basic types of marine batteries:

• Marine Starting Batteries provide quick but powerful spurts of energy over short periods of time and are designed to start the engine and be rapidly recharged by the engine alternator. A starting battery should not be used for trolling motors or powering appliances.
• Marine Deep Cycle Batteries are designed to discharge slowly over a long period of time and to withstand several hundred charging and discharging cycles. A deep cycle battery is the right choice for powering an electric trolling motor and other battery-powered accessories such as audio systems, a windlass, depth finders, fish locators, and applicances. Deep cycle batteries should not be substituted for starting batteries.
• Marine Dual-Purpose Batteries combine the performance of starting and deep cycle battery, and are a good choice on smaller when there’s no room for two batteries. While they're able to perform the tasks of a starting battery and deep cycle battery, they're not as efficient as separate batteries.

Deep Cycle vs. Cranking

If you have an electric trolling motor, thruster, windlass, or other battery powered accessories that draw larger amounts of current, you’ll want a separate deep cycle “house” battery for that purpose. A deep cycle battery is only meant to be used where high rates of discharging and re-charging occur often. A deep cycle battery is constructed differently than a cranking battery, with thicker, heavier plates. The longer, higher amperage requirements of trolling motors and windlasses, for example, would heat and distort the thinner plates of a normal cranking battery.

The cranking battery has more yet thinner plates to give a fast voltage spike to crank an engine, but is not intended to maintain high power output for long periods. Yes, a deep cycle battery can be used to start your motor in a pinch, but a two- or three-battery system is highly recommended to separate the engine battery from the accessory (house) batteries.

The best way to be sure your battery is still good is to have it “load tested.” Most auto parts or battery specialty stores will load test your battery for free and tell you if it’s still serviceable. Just because it’s gone dead once or twice doesn’t necessarily mean it’s no good. The rest of your electrical and charging systems may need some attention as well, as something other than the battery itself may be the cause of the problem.

Replacing Your Boat's Battery

Consult your boat owner’s manual or a marine dealer when replacing a marine battery, and be sure to buy a new battery that is a good match for your boat. Marine batteries are rated by their ampere hour rating, reverse capacity, and marine cranking amps. When shopping for a deep cycle battery, you'll want to pay the most attention to the ampere hour rating and reserve capacity. For starting batteries, focus primarily on the marine cranking amps. Consult all three rankings when searching for a dual-purpose battery.

If you add electrical accessories to your boat, you may need to upgrade to a battery with a higher amp-hour rating, especially if you spend a lot of time trolling with the engine at a very low speed (which results in less charging power from the alternator) or you spend a lot of time beached or at anchor while using accessories like the audio system.

Charging a Marine Battery

Most of us understand that when we are buying a new or used boat, the batteries supplied may not necessarily be top-of-the-line. If they seem to do the job, we don’t think much about them. But in the warmer climates everyday heat is a major enemy of batteries, and can shorten their life considerably. In areas of the country that force us to put boats in storage for the winter, how the battery is cared for during this period is also critical to increasing life expectancy.

It’s best to keep batteries on a regulated “trickle” charger to maintain charge while not in use. A battery that is not charged (and kept charged) can freeze in cold temperatures and a cracked case is the likely result.  A battery is like a lot of things in life—use it or lose it! A car battery will typically last longer than a boat battery because the car is used regularly and the battery stays charged. When it comes to boats, the old adage of a battery’s life being two years is pretty well on the mark. You’ll usually get a heads-up when it’s about to give up on you, with the warning being a “dead” battery one morning or a bit slower cranking speed than you’re used to. You plug in the charger, the battery miraculously comes to life, and you’re off on your trip. You may think a light was left on, or that the radio memory pulled the voltage down. The reality may be that the battery is sulfating, plates are warped, and it no longer takes or holds a charge like it once did.

Tips for Avoiding Battery Problems

• Secure the marine battery with a good battery tray, which should have a base that is screwed or bolted to the boat and either a rigid bracket or a locking strap to hold it to the base. You don’t want the battery banging around in rough water.
• Frequently check the battery terminal connections to make sure they are snug and free of corrosion. Replace the wing nuts often found on marine batteries with nylon locking nuts, which are much less likely to come loose.
• If you use the boat infrequently, use a maintenance-type battery charger to keep the battery fully charged between outings.
• Before off-season storage completely charge the batteries then disconnect the terminals so nothing can draw the battery down. If there’s power available at your storage site, keep the batteries on a battery maintainer/charger through the off-season to continually maintain your batteries. Otherwise remove the batteries from the boat and store them where they can be connected to a maintenance charger.
• Install a cover or “boot” over the top of the positive battery terminal, if one was not installed by the boat builder, even if the battery is in a covered box. The boot prevents sparks and arcing and possible explosion if, for instance, a tool is dropped on the terminal.

Bottom line? Keep your batteries charged, keep the terminals clean, and by all means get out in the boat and “exercise” your electrical system as often as you can!

Read Next: How to Winterize Your Boat

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How to Tell if Your Boat Battery Is Dying — and What to Do About It

April 07, 2023.

When it comes to hitting the open waters, all boat riders want to think about is feeling the breeze through their hair. No one wants to worry about whether their boat will get them safely out and back.

But with a dead boat battery, the boat may not start up at all. Or worse, it could get into the waters only to sputter out before it can return to shore. Not only will that spoil the riders’ day, but it can also be a major liability for boat rental companies. So how can you tell when your boat battery is dying, and what can you do when it is no longer working?

Here’s everything you need to know about boat batteries — from symptoms of a marine battery on its way out to marine battery maintenance.

Symptoms of a Failing Marine Battery

Because boating can be seasonal, your battery may have spent months sitting unused. This can make it tricky to spot the signs of a failing battery. So before anyone ventures too far from the shore, look for these symptoms:

• Slow or no engine turnover. Your boat will likely have no trouble starting up with a newer battery. But as the battery is dying, the engine can take longer and longer to turn over. If it takes more than ten seconds, this is a dying or dead boat battery symptom. A dead battery could also be the culprit if the boat doesn’t start at all. Always seek a professional opinion to ensure it’s not something else, like damaged spark plugs or electrical wires.
• Faulty electronics. Modern boats have a lot of tech integrated for comfort and safety. But if you notice a disruption in the electronics, it could be a sign that the battery is dying. Check your battery if any electronics, from the GPS to the lights, aren’t working.
• Visible damage. Sometimes, you can simply look at a battery and tell something is wrong. A bulging battery indicates acid build-up , while cracking could mean the battery has been overcharging and will lose quality. Either way, the battery will need to be replaced as soon as possible.

Causes of a Spent Boat Battery

Boat batteries can fail for many reasons. Of course, they can naturally reach the end of their useful lifespan, and it will be time to recycle the battery and replace it with a new one. Or, batteries can die prematurely from lack of maintenance or simply sitting unused for too long. If your boat battery is dead, it could be due to the following:

• Corrosion. Over time, corrosion on battery terminals can cause sulfation or a build-up of lead sulfate crystals, which will drain the battery's life. Without regularly inspecting for and cleaning up corrosion, the battery could be vulnerable to sulfation.
• Age. Marine batteries last around 3 or 4 years. Batteries older than that will naturally weaken. If your boat battery shows signs of dying, it may simply be past its prime.
• Parasitic draw. Forgot to turn off the radio or a cabin light? The battery will continue to power anything left on, that is until the battery has died.
• Dormancy. When a boat is left sitting for several weeks or months without use during the off-season, the battery can drain. This is why it’s a good idea to leave your batteries on a trickle charger during the off-season. 

What to Do When You Suspect a Dead Boat Battery

If you think your boat battery is dying, there are a few steps you can take to confirm your suspicions. In most cases, if the battery is dead, it’s time to start thinking about a replacement. Boat batteries have a lifespan of about 3 to 4 years, so if it’s been a while since you replaced the battery, it’s likely time for a new one.

Don't Jump the Battery. With car batteries, you can typically jump the engine to give yourself a little more time before replacing the dead battery. But with marine batteries, attempting to jump the engine with a car battery could damage the boat battery and the boat itself.

Many boats have deep cycle batteries , which help power marine tech on the vehicle, but these batteries won’t recharge after you’ve jumped them. They work differently than standard automotive batteries, and therefore can be damaged from attempting to jump.

Check the Battery Voltage. Check the voltage on the marine battery with a battery tester or voltage meter. Marine batteries should have 12.8 voltage with a full state of charge or around 12.4 with the onboard technical components. 

If the voltage test shows zero volts, the battery has died. But anything under a 12.4 volt reading should raise some concern, and you may want to start shopping for a replacement battery.

Inspect the Battery. Marine batteries are built to withstand all the bumps and vibrations that come with riding on the water. But boat batteries can still wear out or become damaged. If you think the battery is dead, look for cracking, warping or bulging on the battery, which are clear signs of damage. Any of these signs mean it’s time to replace the battery as soon as possible.

Find a Boat Battery Replacement. A dying marine battery isn’t something to take lightly. While many boats have backup batteries in case of an emergency, no one wants to get caught out on the water with a dead battery. If riders end up stranded or need to be towed back to shore, the boat rental company could be held liable.  

If you notice visible damage to the battery, experience symptoms of a dying battery (like slow charging or faulty electronics), or get a poor voltage reading, you should replace the battery before taking the boat out on the water again. 

Find the right marine battery for your vehicle fleet, from starting batteries to deep-cycle batteries to dual-purpose batteries to get you from land to sea and back again.

Boat Battery Maintenance

Once you’ve replaced a spent marine battery, you’ll want to give it some TLC to help it last as long as possible and keep riders safe and happy on their rental boats. With proper maintenance, a boat battery can last around up to six years. Follow these steps to keep your boat battery in great condition for years to come:

• Clean corrosion. Corrosion can naturally occur on the battery terminals from the reaction of battery acid and metal. But over time, corrosion can cause sulfation, which can prematurely kill a battery. Make sure to clean off corrosion with a wire brush or with a cloth and a mixture of water and baking soda.
• Maintain a charge. To extend the life of the marine battery, keep the state of charge to at least 50%. You can check the state of charge with a hydrometer or battery tester. Make sure the tester you use is rated to work with the type of battery your boat has, whether it’s flooded, sealed, absorbent glass mat (AGM) or lithium.
• Mind the temperature. Extreme temperature fluctuations or very cold or hot weather can all shorten the life of a battery. Minimize vehicle use in extreme temperatures, and keep the battery stored in a cool, dry place, ideally somewhere that will not experience temperatures much below freezing point.

Maintain a Healthy Battery for Boat Safety

A dead boat battery is a hassle, especially for those who had planned a fun day full of sun and sea. But if the battery is worn out and dies while on the water, it’s more than just an inconvenience — those on board will have to wait to be towed to shore. And the boat rental company is going to be stuck with the bill and probably some bad business reviews.

The best way to keep riders safe and happy is to make sure your boat batteries are in reliable condition. And when it’s finally time for a replacement, find a high-quality marine battery and keep up with maintenance to help it last as long as possible.

Everything Anglers Should Know about Lithium Marine Batteries

Jason sealock.

• May 03, 2024

The product recommendations on our site are independently chosen by our editors. When you click through our links, we may earn a commission. 

Most of us grew up fishing with lead acid batteries in our boats as our fathers before us did. The new generation of anglers, however, are coming up in the age of lithium marine batteries. Yet it’s somewhat telling how little most anglers know about lithium power. They have seen the literally “inflammatory” stories of the early days of lithium power in boats and have shied away from lithium power. Or they got lithium powered batteries but don’t understand the technology so they are not using it correctly or optimizing its longevity. The lack of people that know about lithium marine batteries and how best to use them caused me to put this together.

I recently wrote an in-depth marine battery guide that covered a bunch of the best lithium batteries in the marine space this year as well as some of the more used lead acid and AGM batteries. I am a big proponent of lithium power for no other reason than the longterm clean power they provide. But I also had a ton to learn about the technology, how they are built, how to maintain them properly and what things can cause anglers issues.

So I reached out to several of the owners and engineers at 4 or 5 of the top companies and had them tell me what they’ve learned over more than a decade of building and refining the technology that is of utmost importance to the owners of these products. The only purpose of this article is to help you make your expensive purpose last as long as humanly possible and have the least amount of hassle with your investment.

LITHIUM POWER IS NOT THE SAME AS LEAD ACID POWER

Lithium batteries are made very differently than lead acid batteries. For starters their cells are all encased. So their is no acid bath to maintain at certain fluid levels or worry with burning up and drying out. The cells in the battery also have controllers called Battery Monitoring Systems (BMS) that monitor and maintain their usage. These controllers are often what varies among manufacturers with many offering Bluetooth compatibility and apps to know how your batteries are doing at all times as well as other add-on features.

Generally inside of a lithium battery there are multiple cells that make up the total voltage. So say in a 12 volt battery like a Dakota Lithium 12V 60Ah battery , you have 4 cells that are each 3.2 volts, to make a total of 12.8 volts for your battery. That’s why you often see 12.8 or 13.2 or something of that nature on your graphs instead of a flat 12 volt reading you would expect.

Manufactures like PowerHouse Lithium actually offer 16-volt batteries so they will use 4 cells with 4.2 volts each. So fully charged your battery is hitting 16.8 volts to start the morning. Some folks are afraid to run a 16-amp battery on their boat for fear it will mess up their electronics. Humminbird’s newer units are actually rated for 20 volts. Most Garmin units are rated for 18 volts, with their 86xx series actually rated for 32 volts. And finally Lowrance is rated for 17 volts. So all of the current graphs are actually rated for higher voltage and this is largely due to the fact that technologies like 360, side scan and live imaging show you more detail with a higher voltage.

Now with lithium batteries, it is important to know your system is only as good as your weakest battery, and your weakest battery is only as good as your weakest cell. It’s also important to know that you never want to deplete your battery fully as the BMS will often put them to sleep when that happens as a precaution and you have to wake them up. Some newer BMS systems have auto wake up features. But most of the time just hooking the battery to a lithium only charger, will automatically wake them up.

In the early days of lithium power, guys would hook incorrect charges to lithium batteries, overcharge them and blow them up. That hasn’t been an issue in more than a decade because the BMS systems monitor that and dedicated lithium chargers are way improved now.

I have a 36V charger from Dakota that is an 18Ah and it’s a beast of a charger. It will cycle a charge in my trolling motor batteries and have them ready to go in an hour or two. It’s crazy how fast these things charge.

Lithium battery chargers work exactly the opposite of conventional chargers. Most conventional chargers are waiting for an input from the battery of usually at least 8 volts. Whereas a lithium charger is not waiting to see the charge back. It’s on all the time. That’s why you hear stories of guys having to “jump their battery” or hooking it to another charger so that their conventional charger sees current coming in to activate.

Nowadays you can just hook your depleted lithium battery up to a dedicated lithium battery charger and it will start charging it. Lithium batteries do not have “memory” like lead acid batteries do. They can sit partially charged or fully charged for a long time with no degrade in performance. They do have a limited number of charge cycles. And that is also a place for confusion we will address later.

UNDERSTANDING AMP HOUR VS VOLTAGE

Before we get too far into the weeds on maintaining lithium batteries, lets cover some basics first that will help as we go further into this resource. Lester Miller, owner of MillerTech Energy spent a bunch of time going through the ins and outs of lithium power with me. MillerTech is a big player in the marine space and an even bigger player in the solar energy industry. So they have a vast knowledge and experience with lithium powers and how it’s best used, and maintained with the least amount of issues. They also offer some of the best service in the industry for customers which is another important factor to keep in mind.

The biggest confusion point for anglers comes in knowing Voltage and Amp hours and what they need to know to choose the right battery. Now a good company like MillerTech is going to work with you to figure out your system and how you fish to help pick the right battery for your boat and your fishing. They are not going to just sell you the most expensive battery.

Voltage is a measurement of overall power and amp hours are a measurement of overall run time. So say your unit or Livescope requires at least 10 Volts to operate but you want to run it all day. So you need that 12 Volt battery fully charged to even use the unit. But as you use it, it’s drawing a certain amount of amps per hour. For some small graphs it might be only 1 amp an hour. So a 50Ah battery can run that small graph for days. However if you have your live wells, two graphs, side scan transducers, lights, Power-Poles all running off that one battery well you might be drawing 10 amps an hour. Now that same battery is only going to get you through about 5 hours.

That’s what a good lithium battery provider will do. They will ask you about your system and then make a recommendation based on their best estimates with their known experience with the draw on certain items on a boat (like a trolling motor, fish finder, imaging transducers, live wells, lights, Power-Poles, and more).

Well how can you achieve more voltage or more amp hours is the next logical question. That’s where we get into the discussion of Serial virus Parallel rigging of multiple batteries.

SERIAL VS PARALLEL FOR VOLTAGE AND AMP HOURS

Basically speaking in terms of lithium power, if you want to increase voltage, you run two or three batteries in series. If you want more amp hours, you run two batteries in parallel. Where a lot of confusion comes in, even among professional anglers, who have been doing this a long time, all we’ve ever had available to us was 12-volt batteries. Now with lithium batteries, you can buy a 24-volt, 36-volt and 48-volt battery if you want. And their are pros and cons to that of course.

Miller talked about one angler he worked with who could just not get their mind wrapped around wanting to run three 12-volt batteries in series to get to 36-volts instead of just running a 36-volt battery.

“BMS are better equipped to run in those voltage environments they were designed for,” Miller said. “What I couldn’t get the angler to understand is that a 36-volt battery’s BMS was built to operate at maximum efficiency in a 36-volt environment. And you have a lot more margin for error and depletion with the battery still operating fully in a 36 volt battery than you do three 12-volts running in a 36 volt system.

By that I mean, a 12-volt battery has a BMS that is optimized to run in a 12-volt environment. And there is a lot less ‘run-up’ there. If your battery has a problem with one cell. You just dropped to nine volts and your 36-volt system is now only as good as your worst battery which is now just running at 9 volts so your system just went to 27 volts. If that battery goes down, your trolling motor is probably not going to work. With the 36 volt battery, you are not going to have near the issues like that. And if you run a parallel 36-volt system you can run for long days, much cleaner and with a less issue-laden 36-volt system because the system is optimized to run in a 36-volt environment.”

After speaking with Miller, I upgraded my own system from three 12-volt batteries on my trolling motor to two 36-volt batteries in parallel. I use my boat all day, and when I plug it into my 36-volt Dakota Lithium charger, I am charged usually in less than 2 hours.

Similarly, I have a Precision Power Lithium 12-volt 100Ah battery that only runs my two graphs and my Livescope. And people ask me all the time why my 8616 screens look so clear and sharp. I have a a Sea Clear Power run wired direct to cutoff switches at the battery. So I’m getting strong clean power all day. If I start fishing super long days, I may go to a parallel system to have constant power for longer days or upgrade to a battery with more voltage to see farther into the water..

Terry Brown runs a 16-volt PowerHouse Lithium battery for his graphs and has some of the cleanest screens you will ever see. Shaye Baker runs a 24-volt MillerTech battery on his trolling motor and loves the all-day power it provides.

Obviously the combination of voltage and amp hours affects the price of the batteries more amp hours and more voltage in a single battery increases the price significantly. But keep in mind you’re talking about powering your boat with these batteries for a decade. But we should delve into the longevity of lithium power along with other issues that might arise as you become a long term owner of lithium power.

ISSUES TO UNDERSTAND IN LITHIUM BATTERIES

Lithium power is mostly full proof from my experience with it over the last 4 years. They biggest issues come from charging in freezing environments, water getting in the batteries, letting the batteries deplete all the way and figuring out when and how much to charge them to avoid using up your charge cycles too fast. So lets tackle all of these here and add some engineering wisdom to some of the myths and opinions that I have seen circulating out there that just are not right.

Freezing Temps

You’ve probably seen the posts or heard people say to never charge your lithium battery in freezing temperatures. That’s actually not bad advice but probably not for the reasons you think. The cells do have liquid in them and that can freeze. But the issue is the build up of water through condensation. Water is maybe the worst thing for a lithium battery cell.

The issue happens when charging a frozen or very cold battery causes the battery to warm up rapidly as it takes the charge from the charger. The rapid warm up of a cold battery causes it to build up condensation inside and that is the problem. It’s not that charging a frozen battery hurts it. It’s the fact that the cold hot cold hot cycle of charging and cold elements causes condensation to form. And that’s a very bad thing.

Miller recommends taking the batteries inside in the winter and charging them. Or keeping the boat in a warmer (non-freezing) storage area and not charging in the coldest environments. PowerHouse Lithium, actually offers the ability to charge down to 23 degrees because of the internal build in their batteries but even they recommend not charging much in the coldest environments as repeated charging at sub-freezing temperatures can reduce the cell life longevity.

Water in batteries

Water causes the biggest issues in lithium batteries. Water causes a volatile reaction when it mixes with lithium called effervescence. It causes hydrogen gas to release and the reaction is thermogenic so it causes a lot of excess heat. That’s why the top lithium marine battery makers create IP6 or IP7 rated waterproof batteries to keep 100% of the water out of the batteries. Not only to prevent the reaction but to prevent corrosion, short circuits to the BMS and increased resistance and electrolyte leakage from the cells.

Creating safe batteries is priority number one for most of the manufacturers we talked with. While there are still some in the insurance world who wish to ban lithium power on watercraft, the risks have thus far been mitigated and for the most part eliminated by today’s highly evolved lithium battery options.

Depleting a battery too much

Running a lithium battery down to zero is also a bad thing. It’s not something you have to worry about as much now with today’s much more refined lithium marine batteries because the BMS sets a cutoff voltage and puts the battery to sleep (i.e. shuts down your system) to prevent it from ever getting too low. Not to get too technical on what happens when a lithium battery full discharges, but basically there is a chemical breakdown that occurs and the battery life of the battery is reduced. So your 10 year battery won’t last 10 years if it were to discharge fully.

While the sleep thing can be a nuisance, it’s fairly simple to avoid and we’ll discuss that in the final section.

Charge cycles

So there are a lot of terms that float around when talking about lithium power. Things like State of Charge and Depth of Charge matter when talking about charge cycles and life span of a battery.

So originally, the thinking was a battery has a certain number of charge cycles before the reaction that happens with the electrodes and the electrolytes has run its course and depleted fully in the battery cells. So because there was a limited number of charge cycles for the battery, many folks told you not to charge your battery after every use to preserve your charge cycles and not limit the life of the lithium battery.

However there are other factors to consider here. State of charge refers to the current capacity of the battery compared to its rated capacity. So an SOC of 100% means its fully charged and an SOC of 0% means its fully discharged.

Depth of Discharge or DOD refers to the amount of discharge in the battery and this can actually be used to increase the charge cycles of a battery. If you only discharge the battery 30% and it still has an SOC of 70%, then your charge cycles go up because they are based on a full charge. So if you are only having to charge it 30% of the way back to full, that’s not a full charge cycle. So you might have 2x or 3x partial charge cycles as compared to the rate full charge cycles.

“I studied the charge cycles and DOD reference materials on the cells we use in our MillerTech batteries and found that if you charge the battery after short uses you will actually get a lot more partial charges out of the batter and your life span might actually increase,” Miller said. “This is again why spec’ing out your system correctly is so important in the beginning. If you have plenty of power and only partially discharge during the day of use, you can have batteries with a lot more partial charge cycles and your system will last longer.”

BEST WAYS TO MAINTAIN YOUR LITHIUM MARINE BATTERIES

Now that you understand how lithium batteries differ from what you may have known from other batteries. It’s worth relaying some more helpful information from Dakota, MillerTech, PowerHouse Lithium and ZPro Lithium.

I have run a mix of lithium batteries in various boats. I have a travel 12-volt Dakota Lithium that I take with me when I’m going to be using other boats like I did at a fish camp this spring in Illinois. I ran a small 12-volt trolling motor. I also have two small lithium batteries that I run in my kayaks. I run a ZPRO 12-volt 50Ah and a Tracker Lithium 12 Volt 50Ah that I run in two different kayaks. I have two 36-Volt RELiON batteries that I run in parallel on my Xpress X21 Pro to power my Garmin Force. I run a Precision Lithium battery as my Electronics battery in that boat. I have a MillerTech cranking battery that I’ve tested as a starting battery but don’t use it currently because it will void my Yamaha Warranty.

I’ve also tested several others that you can see in the Best Marine Battery Guide.

So I’ve been around a lot of Lithium batteries. I’ve used a lot of chargers. I’ve ran a lot of different configurations and at first it can all seem confusing. But the crux of it is to understand your boat, your system needs and how you fish. Those all factor into how much voltage and Amp hours you need and from there you can figure out the best configurations.

To me getting that right is the best way to make sure you have batteries that last a lot of years. If you get too small a battery and you are running it nearly dead every fishing day, then that battery is not going to last as long. But if you run an adequately powered battery for your system and are charging it regularly after partial cycles, your batteries are going to last a long time.

Then take a system like the PowerHouse Lithium where their batteries are monitoring the cells and when it starts seeing one of the cells operating outside of parameters, it alerts you through the app to contact PowerHouse Lithium for support and you send them the screenshot and they make a determination if they should warranty replace the battery or not. That next level of preemptive support is unheard of with battery power in boats.

And Support is another huge piece to making sure the investment in lithium power is worth it. If you spend a lot of extra money on a large lithium battery, than you should reasonably expect a high level of support. That’s why companies like MillerTech, PowerHouse, Dakota, Precision Power and ZPRO are so well liked by pro anglers and avid fishermen alike. Because when you dial the phone, someone answers and can help with your problem.

So it’s definitely worth it to go with a reputable brand that has high levels of support at your disposal.

Some other simple ways to keep your batteries operating at max capacity for as long as possible would include the following:

• Avoid charging your batteries in extreme cold or extreme heat
• Charge your batteries after every use so they only use partial cycles
• Keep your batteries in dry compartments and secured
• Use bigger batteries with more capable BMS when higher voltages are needed
• Run your batteries in Series to increase voltage and run your batteries in parallel to increase amp hours
• Use lithium chargers

Also understand that how you use your equipment figures into your power needs. A guy who fishes in current or grass all day will draw a lot more power a lot faster than a guy who uses the same trolling motor to put around on speed 2 or 3 fishing in relatively clear open water. The harder you run a trolling motor the more it will draw. The more graphs you have, the bigger draw you will have. So again understanding the balance between your power needs and the available battery options will allow you a lot years of worry free power.

The days of worrying about your batteries blowing up and the like are long gone if you follow these simple guidelines. The fact is lithium offers very strong, clean power for long periods of time. They offer wide ranges of options to fit nearly any system. Some of the companies like MillerTech, Dakota, PowerHouse Lithium, Precision Power and ZPRO offer high levels of personal support. That can be one of the biggest factors in having a product for 10 years. Do your research, reach out to the companies and they will help you piece together the appropriate power system for your specific boat and equipment.

Currently working as Senior Advisor to Wired2fish. Former COO and Publisher, Jason Sealock came to Wired2fish shortly after inception in January of 2010. Prior to that he was the Editor-in-Chief of FLW Outdoors Magazines. He worked up from Associate Editor to Photo Editor and finally Editor in Chief of three magazines FLW Bass, FLW Walleye and FLW Saltwater. He set the content direction for Wired2fish while also working directly with programmers, consultants and industry partners. Sealock has been an avid angler for the better part of 40 years and has been writing and shooting fishing and outdoors content for more than 25 years. He is an expert with fishing electronics and technologies and an accomplished angler, photographer, writer and editor. He has taught a lot of people to find fish with their electronics and has been instrumental in teaching these technologies to the masses. He's also the industry authority on new fishing tackle and has personally reviewed more than 10,000 products in his tenure. He has a 30-year background in information technologies and was a certified engineer for a time in Microsoft, Novell, Cisco, and HP. He mostly fishes for bass and panfish around the house. He has, however, caught fish in 42 of the 50 states in the US as well as Costa Rica, Mexico, and Canada and hopes to soon add Finland, Japan, Africa and Australia to his list.

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Practical Boat Owner

• Digital edition

Best boat battery: The pros and cons of the 5 different types of marine batteries

• Alison Wood
• October 28, 2022

Boats usually have two batteries (or banks of batteries) to ensure one is for starting the engine only, and the other to run the domestic systems.

Some marinas, such as Chichester Marina, require a key code for electrical supply. With others, shore power is included in the price

Sometimes (though not on Maximus ) there’s a third set of batteries for high power items such as a bow-thruster or electric windlass.

Wet lead acid

Batteries that have liquid electrolyte sloshing around in them are sometimes referred to as ‘wet’, ‘flooded’ or ‘wet lead acid’ batteries.

To start the engine, boats have a starting or ‘cranking’ battery, like those used in cars, which delivers very high loads for a few seconds.

Only a small portion of the battery’s capacity is used and this is restored by the alternator once the engine is running.

For powering everything else (i.e. chartplotter, lights, fridge, etc.) boats use a domestic, or ‘house’ deep-cycle (or deep-discharge/traction) battery bank which draws a much smaller amount of power over a longer period of time.

It’s important that wet lead acid batteries are stored in a ventilated area. A disadvantage is that they can ‘gas off’ (release hydrogen) if faulty, overcharged or getting old.

Pros: cheap, readily available, lots of choice, starter batteries can be bought in automotive stores. Cons: heavy, can leak, need regular charging, useless once flat, can gas off.

Article continues below…

Which battery is best for my boat? How to increase battery capacity on board

With more and more electrical gear going on board the modern cruising yacht there comes a time when the battery…

Lithium batteries vs lead-acid batteries: What are the key differences for boat owners?

But even the best lithium batteries do have downsides, writes Emrhys Barrell . The first is cost, at up to…

Wet lead acid – dual/leisure battery

An ‘in-between’ option is the ‘dual’ or leisure battery. A compromise between starting and deep-cycle batteries, these are popular on boats that carry only a single battery, or prefer to have the same type of battery for simpler charging.

Maximus had a leisure battery for starting the engine (an 85Ah Green Power) and a 100Ah deep-cycle Lifeline Battery for powering the rest of electrical equipment.

Both were flat after being left on board for two years and so could not be revived.

Pros: cheap, readily available, lots of choice, dual-purpose starter and domestic. Cons: heavy, can leak, need regular charging, useless once run flat, can gas off.

Rolls sealed VRLA deep cycle batteries on the Ecobat stand at Southampton Boat Show

Sealed lead acid batteries (gel & AGM)

Nobody wants battery acid leaking into the bilge, but there’s a price to pay if you want more durable batteries.

Sealed lead acid batteries are sometimes referred to as VRLA (valve regulated lead acid) and there are two main types – absorbed glass mat (AGM), where the battery plates are protected by fine-stranded glass mats – and gel, where the liquid electrolyte has been converted into a gel.

AGM batteries can be used for both starter and house applications whereas gel batteries are better suited for house applications only.

Both types can withstand many more charge/discharge cycles than conventional deep-discharge batteries – for example, a 7-10 year lifespan rather than a 4-5.

Pros: leak-proof, longer lifespan than wet lead acid, AGM can be dual-purpose starter and domestic. Cons: twice the price of wet lead acid, up to 25% heavier, need regular charging, useless once flat.

The extensive lead carbon battery bank for electric narrowboat Old Nick

Lead carbon batteries

Lead carbon batteries are not widely known. Our electrician had never fitted them, and indeed I hadn’t considered these until I spoke to Victron Energy.

However, they are highly regarded by PBO contributor Paul Sumpner, who fitted Leoch lead carbon batteries to his electric-propulsion narrowboat Old Nick .

Paul worked out his requirements, which were a regular DoD of 50%, year-round usage, a minimum of 48V, 600Ah, zero maintenance, a life cycle of 3,000+ discharges, non-vertical mounting and to be able to survive a regular partial state of discharge. Plus, they couldn’t “completely blow the budget”.

Old Nick , Paul Sumpner’s narrowboat, is electrically propelled and runs off lead carbon batteries.

“It became clear that only lead carbon or lithium batteries would be suitable,” he said, and later confirmed he couldn’t be happier with the equipment he chose.

Lead carbon batteries are an advanced type of VRLA battery, which has a positive plate (anode) of lead, but a negative (cathode) plate made of carbon composite.

According to Victron, the advantages are less sulfation, and a lower charge voltage, meaning higher efficiency and less corrosion of the positive plate. Overall, the result should be an improved cycle life.

Pros: leak proof, longer life, less sulfation. Cons: more expensive, can’t be used for starter motor, larger and heavier than AGM or lead acid.

AMPS 100Ah deep cycle lithium-ion battery

Lithium batteries

Lithium-ion is a broad chemistry of batteries, the most common being LiFePO4 (Lithium Iron Phosphate). They can withstand four or five times the number of cycles compared to most deep-cycle lead acid batteries (4,000+), can go down to a much lower state of charge, and can keep a reasonable level of charge for up to 12 months.

While lead acid batteries, in practice, only allow 30% of rated capacity, the best lithium batteries can be discharged to 70-80% of the rated capacity.

So really, a 100Ah lithium battery is the equivalent to having a 200Ah lead acid battery, only it will usually charge much quicker, is half the weight and a lot smaller.

A word of warning, though. Although lithium batteries can accept fluctuating voltage (13.6V-14.6V) like lead acid batteries, they should not be directly charged from an alternator because voltage spikes could damage them. A dedicated charger and battery management system is a necessity.

Pros: long-lasting, can use 80% of capacity, easier to manage, small, lightweight. Cons: expensive (up to 4 x cost of wet lead acid), boat adaptations required.

*Batteries chosen to show a range of brands and prices, not because PBO recommends these over others. Prices include VAT and UK delivery, and are taken from online retailers

Having had a brief look at batteries, I called marine surveyor Ben Sutcliffe-Davies. I wondered if there was any possibility of reviving flat batteries.

“I’ll be honest with you, start with new batteries,” he said. “You’re relying on this battery to start the boat. Yes it might pick up, but I guarantee it’ll be like a dying swan when you need it.”

The new batteries were fitted in a ventilated space below the cockpit

For domestic systems, Ben likes Numax batteries, which he says a lot of the industry use. For the cranker, he said, any automotive battery would do.

“I went down to my local tyre and exhaust place, and just got four heavy-duty deep cycle leisure batteries and one tidy cranker for the engine,” he told me.

Thanks to our Project Boat Supporters

Dell Quay Marine , Osculati , Raymarine , Shakespeare Marine , TruDesign , Screwfix , Coleman Marine Insurance , MDL Marinas , Premier Marinas , seajet , Marine & Industrial , Clean to Gleam , Dometic , West System , Farécla , Navigators Marine , Lewmar , RYA , Aqua Marine , Ecobat , Victron Energy , Scanstrut , T Sails and XP Rigging .

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How To Test if a Deep Cycle Battery Is Bad? (Marine Battery)

By: Author Steve

Posted on Published: January 23, 2022  - Last updated: December 10, 2022

With the sun shining brightly and a breeze blowing gently, you are looking forward to a successful day of fishing.

Now you want to be sure your marine battery will get you and your boat back home. But how can you test your battery to determine if it is a good or a bad battery? 

First, you need to determine the appropriate type of test to use. You have heard of the remarkable accuracy of multimeters in determining if a battery is good or bad.

You have also heard about load tests and their success with car batteries. Now you want to know if a load test will work with a marine battery, as well.

The fish are waiting, so, let’s get started.

Table of Contents

Signs That a Battery Is Bad

Testing a battery with a multimeter, testing a battery with a load tester.

You don’t want to wait to discover if your boat marine battery is bad until you have left the dock. So be sure to check your battery out before you go.

There are some critical signs to look for when deciding if your battery is bad. If the battery has any of these signs, it is time to get a new one.

First, is the battery keeping the electronics onboard your boat powered?

Are you having any problems with your fishfinder? Is your GPS not working? Is your bilge pump malfunctioning? Is your chart plotter inaccurate? 

Are you having problems with your depth finder? If any of these instruments are not working, it is an indication that your battery may be bad and maybe the root cause.

Next, is your engine turning over quickly?

It is the job of the battery to send power to the starter. Any hesitation, engine stalling, or lack of response is a sign that your battery should be checked.

If your battery is going bad, you could be straining your starter and compounding your problem.

Even when your battery supplies sufficient power, there is still a chance that it might be bad. Inspect the battery for bulging, cracks, leakage, and broken or lose cables.

Battery bulges are a sign that the battery may have been charged too many times. Cracks and leakage are signs of a worn-down battery. 

Be sure to replace broken or loose cables or terminals. This will help prevent your battery from working too hard and requiring early replacement. Even new cables should be replaced if they do not provide a firm connection. 

Feel your battery to determine if it is hot. Hot batteries can lead to a burning smell, which can lead to an explosion.

Check your battery with a multimeter   soon after a charge. If the voltage drops significantly, your battery is going bad.

Finally, a load test will verify your suspicion that the battery is bad. If your battery fails a load test, replace it immediately.

A multimeter    is an excellent device to test a battery.

Before you begin your test, be sure you are protected. You will want to be protected in the event of battery leakage or even an explosion. While these are rare occurrences, they are nevertheless possible.

Wear goggles    to protect your eyes and cover your skin. Try to conduct your test in a cool area, especially if your battery feels warm or hot.

Before you begin your test, remove any battery cover. Let the battery set for at least an hour before beginning your test.

• How Much Power does a Deep Cycle Battery Hold?
• At What Amperage Should I Charge My Deep Cycle Battery?
• How To Test A Marine Battery Charger?

With your precautions set, the first step is to configure your multimeter. You will notice setting selections on the face of the device.

Select the “DC voltage” selection with at least fifteen volts or more. Twenty volts is the ideal choice.

Next, connect the red and black multimeter wires to the battery. Connect the red wire to the positive battery terminal. Then, connect the black multimeter wire to the negative battery terminal.

Some multimeters work automatically. If your multimeter is not automatic, simply press the “min/max” button to begin recording the battery voltage.

You can get multiple readings. The multimeter will have a scrolling function to allow you to view the different readings. Your reading should be a minimum of 12.6 to 12.8 volts. 

If you are testing the battery at engine cruise speed, you can expect a higher voltage reading. In this case, look for a reading between 13.2 and 13.4, as this indicates a good marine battery.

A reading of 12.2 is a concern. At this voltage level, the electronics on your boat may not stay powered. At a 12 volt level, your electronics may not turn on at all.

This would result in an unpleasant outing at minimum, with your GPS, radio, fish finder, and other devices not working. At the extreme, you may find yourself being towed back to the dock.

When you take proper precautions, and you use your multimeter    correctly, you can be confident that your electronics will work correctly, and you will make it home safely.

Take a look at this video from Dan Richard Fishing to get a visual description: 

Load testers are inexpensive. A recommended unit is the Steelman Load Tester. This model has a microprocessor, so you can count on an accurate reading. It is durable and includes a convenient digital display.

The purpose of a load test is to determine the ability of the battery to maintain its effectiveness, not to simply determine its charge level. It determines the amps that are produced by a battery that is charged.

When doing a load test, first be sure that your battery is charged to 100 percent. Uninstall the battery before the test. Let the battery remain idle for an entire night.

Once this idle period is complete, connect the load tester    to the battery. Connect the black wire on the load tester    to the negative battery terminal. Then, connect the positive wire to the positive battery terminal.

You will notice a selector on the load tester    with cranking amp selections. Choose the setting that is half of the cranking amps of the battery.

So if your battery has 800 cranking amps, for example, choose 400 on the load tester selector.

Push the start button on the load tester. Run the load test for fifteen seconds. Record the voltage value and the cold cranking amp reading.

Wait two or three minutes, then do the test again. You should strive for three to four tests. This will give you an adequate sample.

You are looking to see if the cold cranking amp value on the load tester decreases to 80 percent of half of the total cold cranking amps of the battery.

For example, if your battery has 800 cranking amps, one half would be 400. Eighty percent of 400 would be 320 cranking amps.

So if your load tester reading is 320 or less cranking amps, you have a bad battery.

The other critical reading is the voltage reading. If the voltage reading on the load tester goes below 12.4 volts, this also indicates that you have a bad battery.

Of course, some load testers make the results even easier for you. These have a display that simply tells you if the battery is good or bad.

So we have looked at three ways to tell if a marine battery is good.  

Before testing the battery, be sure to wear protective clothing. Use goggles to protect your eyes and a shirt with sleeves to protect your skin. 

Start by observing your battery. Look for bulges and cracks. Cracks can lead to the battery leaking. Bulges indicate the possibility of the battery exploding .

A multimeter will measure amperage and the current power of the battery. A load test will reveal if the battery is holding its power .

Consider performing the load test three to four times to get an adequate sample of the ability of the battery.

Once you know your battery is good, you can concentrate on your ultimate goal: reeling in those delicious fish in the deep blue sea!

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Deep Cycle Marine Batteries: A Comprehensive Guide to Choosing the Best

By Gerald, Updated on September 11, 2024

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