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Auxiliary Battery System Calculator

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Fill out the form fields on both stages of the calculator to obtain your auxiliary power’s useable capacity, daily consumption and maximum run time. Detailed instructions can be found on this page below the calculator.


  • This calculator is configured for 12v systems only.
  • Do not mix different battery types (i.e flooded, AGM, gel or lithium).
  • Do not mix different battery sizes or capacities in the same system.


Step 1

Input the device name, power rating (Watts) and the number of hours use per day for multiple devices and press next.

  • Power consumption can be obtained from the data plate on the device.
  • If you do not know the power rating of a device, multiply the maximum current (in Amps) by 12v to obtain Watts (e.g. 4A x 12V = 48W).

Step 2

Input the battery's rated capacity, the number of batteries and the Depth of Discharge (DOD).

  • For DoD, Maximum of 50% for lead acid (flooded, gel or ACM), and up to 100% for lithium.

The calculator will display the usable capacity, daily consumption and maximum run time based on the supplied data.