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3 Types of Boat Batteries

A photo of pack battery for cars and boats.

Batteries, where would we be without them, right? From watches to cell phones to remote controls, and need I say it, vibrating toys, it looks like everything in our lives needs one sort of battery or another. Take the boat, Family Jewels, I inherited from my late Pappy, for instance.

After just leaving (or neglecting-depends on how you look at it) Family Jewels in the boathouse for close to five years, I finally decided to have a boat mechanic come and look at it. On Wifey’s advice, I  had Sabrina, a woman boat mechanic, give her expert service opinion.

Imagine my surprise when, after looking the Family Jewels over, Sabrina advised me to get a new battery for the boat! 

Growing up, I was told batteries and water don’t mix. Now, here was a woman boat mechanic telling me to get a battery for a boat?! Being something of a male-chauvinist (and clueless about boat batteries myself, of course), I took Sabrina to task about things relating to boat batteries.

So, Sabrina Sweetie, what is a boat battery and what can you tell me about boat batteries?

Close up photo of luxury boat's battery.

If you are a boat owner, it is important to be aware of the boat battery. Also sometimes called marine batteries, boats are designed specifically for use on a boat. They have heavier plates and tough construction designed to withstand the vibration and pounding that occurs onboard any powerboat.

Consequently, marine batteries are usually more expensive than automobile batteries. However, as a boat owner, never be tempted to purchase an auto battery instead of a marine battery. On a boat, a marine battery lasts longer and is more reliable than an auto battery.

When boating, a boat battery is an essential part of the boat’s power supply. It is the heart of the boat, powering everything from the engine, and electronics, to the lights, sound systems, and other of the boat’s components.

As such, in summary, a boat battery is a portable power source that can be used for powering electronics, starting engines, and powering other boat components.

The battery needs to be fully charged before use and be checked often to ensure it is still functioning.  So, I wouldn’t advise leaving a boat battery fixed to a boat for close to five years without ever charging it, for example. The more often a battery is used, the more often it needs to be charged.

If your boat’s battery is not fully charged or in good condition, it can be frustrating to find out your boat won’t start. I recommend charging a battery before use and charging it often when in use.

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The good news is that boat batteries are easy to maintain. All you need to do is maintain a regular charging schedule, and make sure you don’t overcharge or undercharge the battery. To do this, you need a battery charger. You can find them in many stores and online.

The life of a boat battery depends on how often it is used, the age of the battery, and the type of boat battery…..

Thanks, darlin’ for that. You mention the type of boat battery. What types of boat batteries are there?

Knowing the types of batteries out there is vital, especially when it comes to choosing or replacing a marine battery. Otherwise, doing so can become a very complicated process.

There are THREE main types of marine batteries, but actually FIVE. Most boats use two different types of batteries for powering navigation, lights, and electronics. These are the engine starting battery and a deep cycle battery.

1. Marine/Boat Starting Batteries (aka Boat Cranking Batteries)

Close up photo of batteries on display.

Also known as boat cranking batteries, marine starting batteries are designed to start the engine and be rapidly recharged by the engine alternator. The purpose of this type of battery is to provide quick but powerful spurts of energy over short periods.

And since starting a boat engine requires a lot of power in short bursts, a boat starting/cranking battery is a lead-acid battery that is made with thinner, more numerous lead plates. The marine cranking amp (MCA) or cranking amp (CA) rating found on a battery’s label ranks the battery’s starting power.

Always check your engine manual for the recommended MCA/CA rating before you buy a starting/cranking battery. Always choose a battery with a rating equal to or greater than the recommended value.

A starting battery should not be used for trolling motors or powering appliances.

2. Marine/Boat Deep Cycle Batteries 

A photo of Optima Yellow Top Battery on a white background.

When you are out boating (or when you eventually do), electric trolling motors, sonar, and other accessories draw power at a slower rate for extended periods. A deep cycle battery is the best boat battery type to use for such deep discharges that are hard on battery plates.

Deep cycle batteries are designed to discharge slowly over a long period and to withstand several hundred charging and discharging cycles.

For purposes of powering an electric trolling motor and other battery-powered accessories, such as audio systems, a windlass, depth finders, fish locators, and appliances, a deep cycle boat battery is your best bet and the right choice. That as it may be, deep cycle batteries should never be substituted for starting batteries.

A deep-cycle battery’s reserve capacity (RC) rating indicates how long it can carry a specific load before running out of charge. Always consider and follow your boat battery’s indicated RC. 

3. Marine/Boat Dual-Purpose Batteries 

Close up photo of dual purpose battery on the white background.

Dual-Purpose batteries combine the performance of starting and deep cycle batteries.  They are a good choice on smaller boats, especially when there’s no room for two batteries.

Beautiful Sweetheart, and, what are the pros (advantages) and cons (disadvantages) of these boat battery types?

Starting/Cranking Boat Batteries 

While great for starting or cranking your boat’s engine, starting/cranking boat batteries have their disadvantages or drawbacks.

Unlike a deep cycle battery, a  boat starting or cranking battery isn’t made to be completely discharged.

Deep Cycle Batteries 

A nanoscale gel deep cycle battery on white background.

A deep cycle battery can withstand many discharge/recharge cycles.

They have fewer but thicker lead plates than cranking batteries and are built to withstand deep cycling.

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Dual-Purpose Boat Batteries 

Without a doubt, the biggest advantage of Dual-Purpose boat batteries is that they combine the performance of both starting and deep cycle batteries. In this regard, they are convenient, especially when it comes to saving space.

However, while they’re able to perform the tasks of a starting battery and a deep cycle battery, their drawback is that they’re reportedly not as efficient as separate batteries.

This is because most dual-purpose batteries won’t start an engine like a boat cranking battery. Neither do they handle as many deep discharge and recharge cycles as a dedicated deep-cycle model.

You mentioned that there are actually SIX boat battery types. Which are the other TWO??

A grey and blue plastic boat battery box isolated on white.

Depending on your research and reading, you find that there are actually SIX types, arguably SEVEN boat battery types.

Based on the chemistry or conducting medium inside of the battery, boat batteries can be further classified, to include AGM (Absorbed Glass Mat), Gel, Lithium, and to some extent, Wet boat battery types.

AGM (absorbed Glass Mat) Boat Batteries

AGM (absorbed Glass Mat) batteries have porous microfiber glass separators compressed between the battery’s positive and negative plates. These are saturated with just enough acid electrolytes to activate the battery.

Their advanced design allows the electrolyte to be suspended near the plates’ active material, which in theory, enhances both their discharge and recharge efficiency.

For this type of battery, the typical absorption voltage range is 14.4 to 15.0 volts; the typical float voltage range is 13.2 to 13.8 volts.

The “beauty” (for lack of a better word) of AGM batteries is that they have a long life, low self-discharge rate, and are good dual-purpose batteries for boaters who require fast recharging and quick starting power, as well as reliable deep-cycle ability.

AGM batteries’ popular usage includes high-performance engine starting, power sports, deep cycle, solar, and storage batteries. For example,  RV batteries, boat batteries, motorcycle batteries, ATV batteries, and UPS & Telecom batteries for generators.

Gel Cell Boat Batteries

Close up photo of black gel cell boat battery.

Coming in a sealed valve-regulated design, Gel batteries are safer to install around people and sensitive electronics. The Gel Cell Battery system is similar to the AGM battery style because the electrolyte is suspended. The electrolyte in a gel cell battery has a silica additive that causes it to set up or stiffen.

The recharge voltages on this type of cell are lower than the other styles of lead-acid batteries. For this type of battery, the typical absorption voltage range is 14.0 to 14.2 volts; the typical float voltage range is 13.1 to 13.3 volts.

If the incorrect battery charger is used on a Gel Cell battery, poor performance and premature failure are certain. Battery chargers with gel profiles will have information either on the unit or in the manual, about gel compatibility.

Please note that Gel batteries are the most sensitive cells when it comes to adverse reactions to over-voltage charging. For boats, Gel batteries are best used in VERY DEEP cycle applications and may last a bit longer in hot weather applications.

Gel batteries are not as common as AGM batteries, but are often found in deep discharge situations such as wheelchair and medical mobility batteries, trolling motor batteries, and RV deep cycle batteries.

The wonder of Gel batteries is that they are spillproof submersible, and leak-proof. In addition, while the design of Gel batteries nearly eliminates gassing, they still need to be vented.

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However, on the downside, this type of battery chemistry needs carefully regulated smart charging to prevent damage.

Lithium Boat Batteries

Lithium boat batteries are generally more expensive than other boat battery chemistry types. Available at a premium, they have more pros over the others and are worth considering as a boat battery type. 

Lithium batteries can be discharged 800 times to 100% at depth of discharge. They can be recharged in a little over an hour and weigh less than lead-acid batteries. Their major drawback is their price tag.

The same cannot be said of the more pro-prone Wet Cell batteries.

Wet Cell Boat Batteries

A red color Wet Cell Boat Battery on white background.

Wet cell batteries use a reservoir of liquid sulfuric acid. As such, they produce hydrogen and oxygen when the battery is being charged. Wet cell batteries allow the gases to escape into the atmosphere. This is unlike Gel Cell and AGM batteries, which recombine the gases and re-introduce them to the system.

Wet cell battery boxes and compartments must be vented to let the gases escape safely.

Interestingly, technically the AGM battery is still considered a wet cell battery.

Boat Batteries Frequently Asked Questions (FAQs) 

Impressed, but still not totally convinced, I asked Sabrina some FAQs about boat batteries-she still had to prove to me her knowledge of boat batteries before I could trust her to touch my Family Jewels. I gave her five…or so of my best.

How long do batteries last on a boat, and how can I extend my battery’s life?

Front view shot of battery on white background.

The average life of a boat battery is around 3-4 years, although they can last up to 6 years in the right conditions. To ensure your battery lasts its full lifespan, keep your batteries connected to a maintenance charger to keep it fully charged.

What battery is recommended for a boat?

In most cases, 12-volt batteries are what you need. In rare cases, other types of batteries are used, like 6-volt or 8-volt batteries, for example. If your boat is a bass boat or bigger, a 12-volt boat battery is your best bet.

Which marine battery is best?

The 6 Best Marine Batteries of 2022 are:

Best Overall: Odyssey Marine Dual Purpose Battery at Amazon. …

Best Budget (Dual Purpose): Bass Pro Shops Battery at Bass Pro Shops. …

Best Budget (Trolling): Mighty Max Deep Cycle Battery at Amazon. …

Best Trolling (Small Motor): Mighty Max Trolling Battery at Amazon.

Your choice will depend on how you use and save power on your boat.

How many cold cranking amps do I need for my boat?

Close up photo of cranking amps for boat.

75-400 amps To get the burst of power needed to start an engine, a cranking battery needs to deliver a large current for a short amount of time–often 75-400 amps for anywhere between 5 and 15 seconds, depending on the boat’s engine.

Is there a difference between deep cycle and marine battery?

Marine batteries may be starting batteries, dual-purpose batteries, or deep cycle batteries. They are usually a hybrid of starting and deep cycle batteries, with lead sponge plates that are coarser and heavier than starting battery plates but not as thick as true deep cycle battery plates.

After she had so satisfactorily answered my FAQs on boat batteries, I let Sabrina service the Family Jewels.

Interestingly, only later, after Sabrina had done a perfect job on the Family Jewels, did I learn that she actually was not just any boat mechanic. Rather, it turns out Sabrina is, in fact, a mechanical engineer who specializes in boats, and went to MIT!