How do I size a Li-ion battery bank for my system?



Sizing a battery bank for an off-grid or mobile power system can get complicated if you don’t have all the information you need to make the right calculations. You will need at least some basic information to get started.

You will need the maximum and continuous draw – in amps or watts – of the devices you want to power. These are usually found somewhere on the device on a sticker or plate that shows the amps and volts of that device or sometimes the power in watts. If you only have the amps and volts you can use the calculations found in our “How to calculate watts–Ohm’s Law” FAQ to figure out how to find the watts of your system.

As an example, let’s just say that our system need to run 10 amps at 120 volts for 3.5 hours.

10 amps x 120 volts = 1200 watts of power.

1200 watts x 3.5 hours = 4200 watt-hours of energy.

Next you need to convert 4200 watts-hours to DC amp-hours. For our example, we will use a 12-volt battery bank.

4200 watts-hours / 12 volts = 350 DC amps-hours of battery energy are needed for our sample application.

Also, the battery needs to be able to deliver 1200 watts/ 12 volts = 100 amps of power.

We will use the 100 amp-hour Battle Born battery to build this system.

350 amp-hours / 100 amp-hours = 3.5

We would need to use 4 100 amp-hour LIFEPO4 Battle Born batteries to power this system.