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:
|Marine Battery Type
|Average Life Expectancy
|Average Charge Cycles
|wet cell (flooded)
|absorbed glass mat (AGM)
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.
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:
- 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.