What Size Of Marine Battery You Should Get

Having an appropriately sized marine battery is essential for the proper functioning of your boat. This will ensure that your battery ensures a snug fit inside your battery compartment to buffer you from all chances of mishaps. When it comes to picking a marine battery, you need to primarily determine the electrical load of the boat. This can provide you with a clear idea regarding your power requirement for cranking up its energy while having adequate power for catering to the different components and accessories of the boat. Once you gain adequate knowledge about the power requirement, it becomes easy to determine the battery size.

While searching for the perfect size of marine battery, you will first be required to identify the ideal group size. This is considered as one of the foremost marine battery specifications which you need to meet up. Every single group indicate the proportions of the power cell housing specified by the Battery Council International (BCI). The length, breadth and height of battery housings are indicated by the standard sizing of marine batteries.

We have assembled below a chart of common group sizes of marine batteries available in the market today:

​Group Size ​Length ​Width ​Height
​22NF ​9-7/16″ ​5-1/2″ ​8-15/16″
​24M ​10-1/4″ ​6-13/16″ ​9-3/4″
​25 ​9-1/16″ ​6-7/8″ ​8-7/8″
​27M ​12-1/2″ ​6-13/16″ ​9-3/4″
​31M ​13″ ​6-13/16″ ​9-7/16″
​34M ​10-1/4″ ​6-13/16″ ​9-7/16″
​35 ​9-1/16″ ​6-7/8″ ​8-7/8″
​65 ​12-1/6″ ​7-9/16″ ​7-9/16″


Marine batteries can be roughly segregated into two sub-types of starting and deep cycle. Here it is imperative to understand that cycle refers to a type of battery which discharges while under use and is simultaneously charged up fully. A light to medium battery can suffice your requirements for about 200-300 cycles whereas a heavy-duty one can instantly multiply the number of useful cycles to an exact double with next to none ill effects.

Starting battery is similar in its mechanism to the type of battery used in your car. It can crank your engine and an alternator subsequently takes care of all the electrical demands which arise as soon as the motor starts running. This also recharges the current drawn out from the battery. Thus, the beginning jolt of electrical power is taken care of by the starting battery over a short span of time.

The electrical demands of a boat is different from that of a car as it spends long spans of time on a mooring or while being anchored to something. In such a scenario, you will wish to have the cabin lights switched on although the engine might not be running. These activities tend to drain down batteries with no source of replenishment unless the vessel is plugged to shore power or the battery charger is turned on. This is where deep cycle batteries come in with thicker plates which can be repeatedly discharged to about 50% of its entire capacity without causing any damage.


Boats come in a plethora of shapes and sizes. They also have various types of accessories which can be powered to perfection with the right kind of battery. The size of the battery shares a direct correlation with electrical load as well as the boat capacity.