How this calculator works
Convert the application load to current and multiply by the required duration. Increase the result to leave a reserve. The chemistry presets are editable planning conventions through custom mode, not universal discharge limits. Check the actual battery specification and include inverter losses in load power.
Formula
Q = Pt/[V(1-r)]; I = P/V; remaining charge = rQ, where r is the reserved fraction.
Worked example
A 60 W load at 12 V draws 5 A. Four hours requires 20 Ah of delivered charge. With a 50% reserve, choose at least 40 Ah.
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Frequently asked questions
Why does lead-acid use a larger reserve?
A shallow discharge is a common planning choice for cycle life. Manufacturer limits override the preset.
Does this include Peukert effects?
No. High discharge rates can reduce usable lead-acid capacity; use a manufacturer discharge table for final sizing.
How do I include an inverter?
Divide the AC load by inverter efficiency and add standby power before entering the application load.