Calculator 03 · Backup power
Portable power station runtime calculator
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.
Worked examples
Runtime from a 1,000 Wh power station
The examples reserve 10% of the battery and assume 85% conversion efficiency, leaving about 765 Wh for the connected load.
| Example load | Average watts | Estimated runtime | Check separately |
|---|---|---|---|
| Wi-Fi router + modem | 20 W | 38.3 hours | Provider network power |
| Laptop | 65 W | 11.8 hours | Charger and screen load |
| Television | 100 W | 7.7 hours | Connected devices |
| Refrigerator | 120 W average | 6.4 hours | Compressor surge |
Prefilled calculators
Choose a backup power scenario
Start with a realistic load and battery capacity, then replace the defaults with your own equipment specifications.
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.