Battery Runtime Calculator: Turn Watt-Hours Into Realistic Backup Time

Mon, 04 May 2026 00:00:00 +0000

Runtime estimates are simple until the fine print shows up. The useful version includes usable capacity, inverter losses, reserve, and load behavior.

The simple formula

usable watt-hours / load watts = runtime hours

If you have 1,000 usable Wh and a 100-watt load, the simple answer is 10 hours.

The real answer may be lower because of inverter losses, standby draw, cold temperatures, battery reserve settings, and loads that surge or cycle.