What Size Battery Do I Need for My Boat? (Chart)

What size battery do I need for my boat is one of the crucial questions for boat owners. It is necessary to determine the boat’s electrical load to know how much power you need. Only the battery of the right type and size fits the battery compartment, provides enough power to your vessel, and allows the boat to work well.

As you can expect, larger boats will require more sizable batteries. Nowadays, you can find numerous models on the market, so selecting the right one is an overwhelming task, particularly when you are not an expert. So, let’s take a look at this issue.


Choosing the Suitable Battery Size

Choosing the Suitable Battery Size

Nowadays, the marine industry has impressive growth worldwide, so you can expect the batteries demand to rise in the future significantly. As a result, finding a suitable power cell for the boat can be confusing.

The battery size directly depends on the power levels your boat needs. In other words, large boats with powerful electrical loads require larger power cell sizes.

Having an overpowered or underpowered battery will damage the boat’s electronic equipment over time. Therefore, manufacturers recommend picking out the right power cell size.

In other words, you should determine how much power the engine needs to start working and run its electrical components. The best way to choose the correct battery for your boat is to check a few things, like:

  • Determine the boat type you have
  • Determine the battery type for your boat and its physical size and weight
  • Measure the amperage your boat needs
  • Calculate the cells number required and check whether you need more than one battery to run your boat
  • Choose adequate battery technology

BCI (Battery Council International)

Since you need a battery that will fit in the intended place in your boat, the Battery Council International created a chart that defines different battery size groups. That space will depend on the manufacturer and the boat style, so you need to choose a power cell of adequate size.

Each battery has a clearly defined length, height, and width, allowing you to pick out the exact size you need, regardless of the manufacturer.

Marine batteries’ standard sizes

Size Length Height Width
22 NF 9.4 inches (24 cm) 8.9 inches (22.7 cm) 5.5 inches (14 cm)
24 M 10.2 inches (26 cm) 9.7 inches (24.8 cm) 6.8 inches (17.3 cm)
25 9 inches (23 cm) 8.9 inches (22.5 cm) 6.9 inches (17.5 cm)
27 M 12.5 inches (31.7 cm) 9.7 inches (24.8 cm) 6.8 inches (17.3 cm)
31 M 13 inches (33 cm) 9.4 inches (24 cm) 6.8 inches (17.3 cm)
34 M 10.2 inches (26 cm) 9.4 inches (24 cm) 6.8 inches (17.3 cm)
35 9 inches (23 cm) 8.9 inches (22.5 cm) 6.9 inches (17.5 cm)
65 12 inches (30.6 cm) 7.6 inches (19.2 cm) 7.6 inches (19.2 cm)

The quickest way to determine the adequate power cell size for your boat is to check the old battery. Look at a spec label with all necessary information and find the number with a sign BCI next to it that shows the battery category size.

If you can’t find it, the next option is to check the owner’s paperwork with a listed battery category. Your last chance to identify the suitable power cell without these documents is a boat mechanic.

Be careful with boat experts since some can advise you to choose a battery a few categories up or down the scale.

That can be risky since their power strength is the same, but the dimensions are different. It is crucial to pick out the battery that sits securely in the tray and doesn’t interfere with devices around it.

What is a letter M?

What is a letter M

Be careful when buying a battery for your boat you use at a river or lake. In that case, you should avoid the one with the letter M next to its size since it refers to a specific category designed for marine use only.

If you want to sail on the sea, you should choose this particular battery since any other model won’t last long. A non-marine battery will rapidly corrode and fail after regular exposure to saltwater.


Other Boat Battery Specifications

The right battery type

The right battery type

As you probably know, the battery you should buy for your boat needs to fulfill three different tasks:

  • To start the boat engine
  • To power boat’s electrical components
  • To power boat’s accessories

It also needs to keep up with the boat demands and ensure that the vessel provides the necessary performance. Therefore, buying the correct battery type with the proper specifications and suitable chemistry is crucial.

Besides a battery’s proper size, you should pay attention to the design for specific use. You can find three power cell types on the current market, including:

Starting battery – This type powers all the electronics and effortlessly runs the engine. Since it charges slowly, you can expect it to produce high power in short bursts. Most varieties will deliver 75 to 400 A (amperes) for 5 to 15 seconds.

Deep cycle battery – It provides a steady power stream for an extended period. As a result, this model has longer runtime thanks to its capability of larger power storage.

Combo battery – Dual-purpose battery type combines the first two types, and not many engines use it. However, it is an excellent option to start the motor and run the electrical in small boats with only one battery.

Selecting the right power cell type is crucial for the overall boat’s performance. Therefore, it is vital to pick out a replacement battery of the same type as the old one.

Marine battery technology

Marine battery technology

Besides an adequate battery size, you also need to choose the right marine battery technology. It is possible to find four leading battery types on the current market, allowing you to pick out the best option for your boat.

Lead (flooded) batteries – This type has high power output, is easily rechargeable, and is cost-effective. On the other hand, it charges slowly, has a low power density, and requires high maintenance because it is prone to corrosion.

AGM (Absorbed Glass Mat battery) – This battery type with high power output charges five times faster than the lead one. On the other hand, it can only discharge up to 50%, and overcharging or undercharging will shorten its life expectancy.

GEL battery – You can use this maintenance-free battery even in the case of limited ventilation, but high temperatures can quickly damage it. It has the lowest cost per cycle, but overcharging or undercharging will significantly lower its life expectancy.

Lithium-Ion battery – This lightweight, maintenance-free battery type is the most expensive. However, it has the longest life expectancy, and you can use it in places with limited ventilation. Remember that you should buy regulators to prevent undercharging and overcharging and prolong batery’s life expectancy.

The batteries number

The batteries number

How many power cells your boat needs will primarily depend on its size.

  • Boats under 14 feet (4.3 m) long typically require one battery.
  • Boats 15 to 23 feet (4.6 – 7 m) long have a single engine and require two batteries. An exception is vessels with trolling motors that need three batteries.
  • Boats longer than 24 feet (7.3 m) with more than one engine require at least three batteries. Plus, you need to add one more battery for every additional motor.

Design and maintenance

Ideally, you should pick out the durable and maintenance-free power cell. Such a battery provides a longer service life, is convenient, and reduces maintenance expenses.

Reserve power cell capacity

This feature indicates the time a fully charged power cell can stand on its own. Practically it is the power a battery provides to your boat until dropping below 10.5 volts.

As you can guess, you will need a higher reserve capacity to run the electrical grid when you have a boat with a larger electrical load.

CCA (cold-cranking amps)

CCA (cold-cranking amps)

Always consider the marine battery’s CCA since low temperatures make it hard for a marine battery to start the boat’s engine.

In other words, a battery with a higher cold cranking amps rating is a better option for your vessel if you live in a cold region. It will provide enough power to start the engine when it is cold outside.

The manufacturing date

The manufacturing date will show you how long the power cell can last. That way, you will estimate the framework period of how long you can use it from the moment of purchase. Your goal is to buy the one that will work for years. Otherwise, you will get stuck with a bad investment.


A warranty will keep you from purchasing a low-quality battery and reduce future maintenance costs. Only that way will you get the manufacturer’s support and free repairs and replacements when necessary.



Once you need to replace a power cell in your boat, you will face several questions, including appropriate battery size. However, you should also check the required type and specific features, depending on the use you have on your mind.

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