Battery Runtime Calculator (Load Current)

Naive runtime is capacity divided by current, but three real-world factors shave it: inverter/converter efficiency (85-95 percent), Peukert derating on lead-acid at high rates (up to 30 percent), and unusable capacity below the cutoff voltage. The calculator folds them in. Example: a 100 Ah AGM battery feeding a 20 A inverter load nominally runs 5 h; with Peukert 1.25 and 85 percent efficiency, expect about 3.6 h before the 10.5 V cutoff. Check the inverter floor: lead-acid banks cut off near 10.5 V for 12 V systems, stranding the bottom 20 percent of charge, while lithium BMS units cut at 10-11 V but deliver most of the label.

1. 1

   Enter battery capacity

   Ah from the label.

2. 2

   Enter load current

   Average amps drawn.

3. 3

   Set efficiency

   Or accept the realistic default.

• Using label Ah at a discharge rate the battery cannot sustain

• Ignoring the inverter's own idle draw, which matters on light loads

• Treating lithium and lead-acid derating as identical