The batteries used for powering electrics such as lighting and appliances inside a boat or campervan might appear the same as those used for starting the engine, both are 12V and are available in the same sizes, however they are designed for different purposes. Below we will look at the different types of batteries, the different ratings used to compare them and how they can be installed in an electrical system.
Used for starting the engine of the vehicle, these are designed to provide a very high current output over a short time while the starter motor is running. The design of these batteries means that while they are excellent at providing this high current, they are not able to withstand being deeply discharged without suffering damage.
Leisure batteries (also known as house batteries or deep cycle batteries) are designed to provide a lower current output over a longer time, perfect for boats and campervans that need to run low power devices such as lighting. These batteries have a higher maximum discharge tolerance, with up to 50% total discharge of their rated capacity during normal operation.
The power ratings are found printed on the top or sides of a battery, the two most popular ratings being Amp-hours (Ah) and cold cranking amps (CCA).
The main factor to consider when choosing a battery, as well as chemistry, is size. The size of the battery (or battery bank) should be based on how much power you are expected to use (in Ah) throughout the day, and how much power will be put back into the battery from sources such as solar panels or a battery charger.
Calculating battery size required
When selecting a batteries capacity for your electrical system you will need to calculate both the power used in a 24hr period (in Ah), and how many Ahs of charge will be put back into the battery in the same 24hr period.
From this example a lead acid battery will need to be a minimum of 100Ah to be suitable for this usage scenario, while a lithium battery will need to be sized around 55-60Ah.
Remember, lead acid leisure batteries can only be discharged to around 50% of their total capacity before they risk being damaged, so the total capacity must be double the capacity you require.
Multiple batteries can be wired up using parallel or series connections depending on user preferences and other devices that will be used in the system.
Whether a series or parallel system is used, the total available power remains the same.
For example, two 12v 100Ah batteries in parallel will result in a total of 2400Wh in available power (12 X 200 = 2400)
The same 12v 100Ah batteries in a series system will still result in 2400Wh in available power (24 x 100 = 2400)
2x 100Ah 12V batteries in parallel
2x 100Ah 12V batteries in series