Home Power Facts How we calculate runtime
Runtime = usable capacity ÷ average draw. Usable capacity is the energy that actually reaches the AC outlets, which is always less than the rated watt-hours on the box.
1. Usable capacity, not rated capacity
Converting battery DC power to 120 V AC loses energy, and batteries stop before 0%. Independent tests of portable power stations have measured roughly 54% to 90% of rated capacity at the AC outlets. When an independent measurement exists for a model, we use it and link it. When none exists, we assume 80% of rated capacity and label the result "(est.)".
2. Average draw
Appliances that cycle on and off (refrigerators, freezers) are averaged over a day from their daily energy use (kWh/day ÷ 24). Everything else uses its running watts. When an independent test has measured a power station's own idle draw (its inverter running with nothing plugged in), we add it to the load, because it drains the battery for as long as the station is on. Each appliance's figures and sources are shown on its page.
3. Can it run it at all?
A power station can run a load only if all three hold:
- Total running watts stay within the inverter's continuous rating.
- Running watts plus the largest motor's extra startup surge stay within the surge rating.
- The load runs on 120 V, or, for 240 V loads such as well pumps, the model officially supplies 120/240 V split-phase.
4. Sources and verification
Specs come from manufacturers' US product pages, manuals and warranty pages, plus independent tests. When sources disagree we use the manufacturer's current official figure and note the conflict next to the value. Every number links to its source and carries a verification date. We do not test products hands-on.
5. How we make money
Some links are affiliate links. Commissions never change the math or which models appear: every model we track is evaluated the same way.