How this calculation works
- Usable energy = capacity × (starting charge − reserve). Capacity is a manufacturer spec; charge and reserve are your inputs.
- Delivered energy = usable energy × conversion efficiency. Efficiency is a planning assumption.
- Average load = running watts × duty cycle. Your input, or a labeled typical value.
- Estimated runtime = delivered energy ÷ average load. Calculated estimate.
Real runtime also depends on battery temperature and age, the station's own standby draw, and how the load actually varies. Many products marketed as "solar generators" are battery power stations that can be recharged from solar panels — the battery stores energy; it doesn't generate it.
Planning a purchase instead? Use the Solar Generator Size Calculator. Using a fuel generator? See the Generator Runtime Calculator.
Power station runtime FAQ
›How do I calculate power station runtime?
Multiply the battery capacity (Wh) by the share of charge you'll actually use (starting charge minus reserve), multiply by the conversion efficiency, then divide by the device's average watts. Example: 1,000 Wh × 90% × 85% ÷ 100 W ≈ 7.7 hours.
›Why doesn't a 1,000Wh battery provide exactly 1,000Wh to appliances?
Some energy is lost as heat when the station converts battery power to AC (its inverter) or to USB/DC. Many people also keep a reserve rather than draining to 0%. The efficiency here is a planning assumption you can change — it is not a manufacturer specification for any station.
›How long will a 1,000Wh power station last?
It depends entirely on the load. Under this calculator's default assumptions (100% start, 10% reserve, 85% AC efficiency) a 1,000 Wh station delivers about 765 Wh: roughly 38 hours on a 20 W router, about 7.7 hours on a 100 W load, and about half an hour on a 1,500 W heater.
›Why do refrigerators need duty-cycle estimates?
A fridge compressor switches on and off to hold temperature, so it draws its running watts only part of each hour. The duty cycle is the share of time it's on. It varies with the model, room temperature and door openings, so the suggested value is an editable assumption — a watt meter measuring over 24 hours gives the best number.
›What is the difference between running watts and startup watts?
Running watts are what a device draws once it's going. Motors and compressors briefly draw much more to start — the startup or surge watts. A station must cover running watts with its continuous output and the startup spike with its surge rating. Passing both checks still doesn't guarantee every motor will start.