What do you want the battery for?

If your battery usage involves the substantial use of onboard equipment, please take a few minutes to read this page. 

Essentially, you need to calculate how much power you take from your battery/batteries before you are able to recharge them.

Below is a simple way to make this calculation. It will ensure that you protect your investment and obtain the maximum possible life from your batteries:-

1. Make an inventory of the equipment you are running with your batteries e.g. fluorescent lights, refrigerator, TV, Autopilot etc.
2. Write down the power consumption of each piece of equipment (this will be shown on the equipment as Watts consumed.)
3. Estimate how long you use that equipment for, between battery recharges.
4. Simply divide the total equipment Wattage requirement by the voltage of your battery to get the number of Amps that the equipment uses to operate.
5. Then multiply the number of Amps by the length of time you are using the equipment between battery charges, this will tell you how much battery capacity you require in Amp Hours.

Below is an example of the sort of table you can create for yourself and the calculations needed to come to a total Amp Hour requirement.

You have now found that you require a battery capacity of 153 Amp hours to run your equipment including a 33% margin for error or varying usage.

You are now in a position to choose a battery with sufficient Amp Hour capacity to cope with the total requirement you have just calculated, but also take into account your physical space availability.