How Long Do Marine Batteries Last?

How long a marine battery will last depends on what type it is, its capacity, how many cycles it can endure, and how well or badly it is maintained.

Charge-discharge cycles: 200-600 cycles (200-300 if light-medium, 400-600 if heavy duty), but some can give up to 1000 or 2000 if it’s a lithium-ion battery.

Capacity: Typical range for AGM is 75Ah to 150Ah (average 100Ah as the most common), but some can go higher, although this declines with age. Lithium-ion ones can provide 4-5 times more cycling than heavy-duty AGM marine batteries.

Years: AGM marine batteries can last up to 8-10 years if well-maintained; otherwise, they last around five years. Lithium-ion ones can last up to 20 years.

Tip: Don’t discharge more than 50-70% to ensure longevity.

I’ll go into more detail below.

Contents

Marine Batteries

Marine batteries refer to those batteries used in marine and marine-related applications.

They are especially used in boats, yachts, and barges. I’ve also given some examples of marine use batteries to show how long they can last.

Ideal Marine Batteries

Batteries suitable for marine use should be able to cope with the conditions the boats are exposed to.

An ideal marine battery can withstand vibration and pounding and is a deep-cycle battery. With these essential features in mind, marine batteries are usually either one of the following three types:

Starting (or cranking) marine batteries provide powerful and instant electrical energy and can be quickly recharged by the alternator. They have thin plates and should not be used for trolling motors.
Deep-cycle marine batteries are specially designed to discharge slowly and withstand lots of charge-discharge cycles. They have thicker plates and can be used for trolling motors.
Dual-purpose marine batteries combine both of the above. They are a good choice when you don’t have enough room for multiple batteries, but they are less efficient overall.

To see how long marine batteries last, I will consider different types commonly utilized for marine use and by function, capacity, and maintenance.

Marine Battery Features

Besides the years a marine battery is expected to last, two key features define its longevity: charge cycles and capacity.

Charge Cycles

One indicator of a marine battery’s lifespan is the number of charge cycles.

This gives a more accurate indication than stating the number of years because it depends on how often you use the battery.

As a general guide, a light to medium-duty marine battery would allow between 200 and 300 charge cycles. A heavier-duty battery would allow roughly 400 to 600 charge cycles. But some manufacturers claim up to around 1000 cycles and even double that with the lithium-ion type.

So, you can expect the charge cycles to range between 200 and 600 cycles depending on the type of battery.

Capacity

The Ah (ampere hour) rating indicates a battery’s capacity.

This gives another indication of how long the battery will last, but you have to take the usage or load into account.

For example, a 100Ah battery can last around 20 hours to deliver five amps but only one hour if used for 100 amps.

In practice, you shouldn’t discharge a deep-cycle marine battery more than 50-70% of its capacity (if you want to preserve its lifespan), so the number of hours will be less. The functional capacity of a 100-amp marine battery would be around 50 amps but only initially, as this will decline as the battery ages.

If you need a marine battery to last longer than the time you’re getting presently, buy one with a higher Ah rating.

Types of Marine Batteries

How long a marine battery will last depends on the battery type, as there are multiple options.

Each type offers certain benefits and operates optimally under certain conditions. They include lead-acid, gel lead-acid, lithium-ion, and AGM. But I’ve given AGM a greater focus because it’s the most common type for marine use.

AGM Marine Batteries

AGM (Absorbed Glass Mat) marine batteries have absorbable electrolyte and fiberglass plates.

This design makes them more flexible than standard wet-cell marine batteries. Although not as spill-proof as gel-type marine batteries, they can still be mounted more flexibly and don’t require maintenance either.

AGM marine batteries offer several more advantages over other types of batteries, making them ideal for marine use. In particular:

They allow the marine battery to charge up to five times quicker than an ordinary lead-acid marine battery.
They offer better protection against leaks, although not as much as gel-based marine batteries.
Although they last about as long as gel-based marine batteries, they don’t deteriorate rapidly like the latter.
They provide powerful bursts of starting amps, which makes them popular when you need to ensure the vessel starts easily.
They are generally more reliable than their gel-based alternative marine batteries.
They are cheaper than gel and lithium-based alternatives.

Here are a few examples of AGM batteries suitable for marine use:

siga AM solar battery — *Siga AM Solar Battery*

solarfam AGM battery — *Solarfam AGM Battery*

The Siga AGM battery is specially made for solar-powered applications but can also be used for marine applications. It’s a 100Ah airproof-sealed battery with fire and sparks protection and extra thick plates to facilitate deep discharging.

It has up to 1000 charge cycles. The manufacturer claims it can last about ten years if you don’t discharge more than 50%.

The Solarfam AGM battery provides a greater 150Ah and is specially designed for camping and caravans, i.e., “small isolated installations.” It, too, can be used for marine applications.

It offers high-energy density and high corrosion resistance. It is designed to last ten years.

One high-end AGM marine battery, shown below, is designed to provide maximum runtime (187-249 Ah) and high cycle life (not specified):

Lithium-Ion Marine Batteries

Some manufacturers also offer lithium-ion marine batteries for marine use.

They are generally small and lightweight (about 40% of lead-acid batteries), making them ideal for small boats. They are good for having long-lasting marine batteries, which can be as much as 10 to 20 years if taken proper care of.

However, they are far more expensive, so they are considered investments that offer long-term savings. Here’s one example:

The “Exide EV1600 Equipment Li-Ion Marine and Leisure Battery 125Ah” costs around $3000.

The price may be prohibitive for small boat owners, but it offers super fast charging in 2 hours and a charge cycle of 2000 cycles. It can last 4-5 times as long as a heavy-duty AGM battery. It also incorporates a BMS (Battery Management System) to prevent high current issues.

Cheaper Li-Ion models are also available at around one-third of this price, but you will compromise with the features and potential longevity.

Gel Lead-Acid Marine Batteries

This type contains gel to suspend the electrolyte inside the marine battery.

The design allows electrons to flow through the gel between plates. Gel-based lead-acid marine batteries require less maintenance than regular ones and offer leak protection. But they can still leak if the case cracks (unlike AGM batteries).

Another key advantage of gel marine batteries is their ability to tolerate extreme temperatures, especially cold temperatures, that would otherwise shorten their lifespan.

Like AGM batteries, although they offer several advantages over ordinary flooded lead-acid batteries and are good for marine use, they are more expensive.

Flooded Lead-Acid Marine Batteries

This is not an ideal type for a marine battery.

Although more affordable than other battery types, it is tempting to use them, but I don’t recommend using them at all for marine use.

Ordinary flooded or wet-cell type lead-acid batteries are more commonly used in automobiles. They are unsuitable for marine use because they cannot withstand constant vibration and vertical movements. Sealed-type batteries are much safer, although more expensive.

Flooded batteries are also very heavy, which is not ideal, especially in a small boat.

However, if you use one, you can expect it to last no more than three years generally and a maximum of 5 years only if very well maintained (which will be difficult in a boat).

Cranking Marine Batteries

Cranking marine batteries are not deep-cycle but are specially designed for cranking only.

The above example (Optima BTDCM 5.5 Marine AGM Battery) is a 75Ah battery.

It is spill-proof, maintenance-free, and offers more than 15 times vibration resistance and up to two times longer life than ordinary lead-acid batteries.

Tips for Prolonging the Life of Marine Batteries

Here are a few tips to prolong the life of your marine battery:

Secure the marine battery to a good tray bolted or screwed to the boat. It will serve as a base and help to hold the battery rigidly.
Use nylon locking nuts instead of wing nuts, as they are less likely to loosen due to the constant movement.
Check the terminal connections regularly to ensure there is no buildup of corrosion. Clean them if you see even a small amount after removing the connectors. Then, smear some petroleum jelly on the terminals to prevent the buildup of corrosion again, although it could take longer to remove the battery next time.
Ensure a boot covers its positive terminal to prevent sparks and arcing. Some have one already, but you should put it over the terminal in case it doesn’t, even if the battery is inside a box.
Disconnect the battery if the boat is not used for a long time. Connect it to a trickle charger during off-season periods.

Maintaining AGM Marine Batteries

If you have an AGM marine battery, you should also protect it from being overcharged and undercharged.

Over- and undercharging can both affect the performance and lifespan of AGM marine batteries. It could shorten their lifecycle significantly. Limit the discharge to no more than 50-70% for best performance and longevity.