Home / Runtime calculator
Battery runtime calculator
Enter the battery's rated amp-hours, its nominal voltage, the load in watts and how far you are willing to discharge it. The result accounts for inverter losses, because the number on the box never does.
Estimated runtime
—
Usable energy
Average draw
Lead-acid: keep depth of discharge at 50% for daily use. LiFePO4: 80-90% is fine. Efficiency covers inverter losses only — add wiring losses if the run is long.
Reading the result honestly
This is a steady-load estimate. A fridge cycles, a kettle surges, and lead-acid loses capacity in the cold and as it ages — a three-year-old flooded pack may deliver 70% of its rated amp-hours. Treat the figure as a ceiling and size the bank above your worst night, not your average one.
Related: what amp-hours actually measure · group size chart