Calculating Battery Runtime

  • by

Battery runtime can be calculated using 1 of 2 methods, dependent upon the type of load the host equipment is placing on the battery.

Constant Current Load

If a battery is put under a constant load, run time should be calculated based on the capacity(Ah) of the battery pack:

Example 1)
A 4S2P battery constructed from 3.6V,3Ah cells is used in a 500mA load.
Capacity of battery pack = 2 x 3Ah = 6Ah.
Runtime of battery = 6Ah / 0.5A = 12 hour runtime.

Example 2)
A 10S4P battery constructed from 3.6V,3Ah cells is used in a 24A load.
Capacity of battery pack = 4 x 3Ah = 12Ah.
Runtime of battery = 12Ah / 24A = 0.5 hour runtime.

Constant Power Load

If a battery is put under a constant power load, run time should be calculated based on the energy(Wh) of the battery pack:

Example 1)
A 4S2P battery constructed from 3.6V,3Ah cells is used in a 7.2W load.
Energy of battery pack = 4x 3.6V x 2 x 3Ah = 86.4Wh.
Runtime of battery = 86.4Wh / 7.2W = 12 hour runtime.

Example 2)
A 10S4P battery constructed from 3.6V,3Ah cells is used in an 864W load.
Energy of battery pack = 10x 3.6V x 4 x 3Ah = 432Wh.
Runtime of battery = 432Wh / 864W = 0.5 hour runtime.