Calculator 03 · Backup power
How long will your power station run it?
Estimate steady-load runtime using rated watt-hours, average device load, system efficiency and the battery reserve you want to keep.
Backup power runtime
Estimate steady-load runtime after inverter losses and a safety reserve.
Runtime = capacity × efficiency × usable battery share ÷ average load. Motor surge, temperature, battery age and device cycling can change real-world runtime.
Battery capacity is only the starting number.
A 1,000 Wh battery does not deliver every rated watt-hour through an AC outlet. Inverter conversion, temperature, battery age and a sensible reserve all reduce usable energy.
Average watts versus surge watts
Runtime uses average load. Refrigerators, pumps and power tools can draw a much higher surge when motors start, so the power station’s continuous and surge output must both support the device.
For critical equipment
Do not rely on a planning estimate as the only backup for medical, safety or communications equipment. Test the full setup under a controlled load and follow the equipment manufacturer’s guidance.