Power Station Runtime Calculator

A power station box makes one promise: this many watt-hours. What it never tells you is how many of them you actually get, or how long your gear runs on them. Inverter losses and the reserve the battery keeps take roughly 15% off the top, and the runtime charts in the ads are drawn at loads no camp has ever drawn. This page does the honest version of the math: pick the thing you run, say how long you need it, and see how long each of the three two-kilowatt stations in our scored comparison actually carries it.

Run your load

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How the math works

Usable energy is the nameplate watt-hours times 0.85 — the share that survives the inverter and the battery’s own reserve on AC power. Runtime is usable energy divided by your draw. That is the whole formula, and it is deliberately less flattering than the makers’ versions, which tend to divide the full nameplate by the smallest load they can photograph. Worked example, the default above: a CPAP with the humidifier on draws 55 W. The Bluetti’s usable 1,763 Wh divided by 55 W is about 32 hours — four full nights on one charge, which matches what our comparison found by the fridge route as well.

Two things bend the number in the real world. Cold bends it down: a lithium battery at freezing gives back less than it holds, and it should not be charged below freezing at all — the same cold physics that kills a canister stove. And storage bends it over months: a station left full or empty on a shelf ages faster than one parked at a partial charge, which is why our lithium battery storage guide applies to a 2 kWh box exactly as it does to a headlamp cell.

The small end of the same problem

Most field loads are not fridge-sized. A headlamp, a lantern and a pair of radios sip where a CPAP drinks, and they have their own dishonest box numbers: our Headlamp Reality Check translates lumens into hours on the battery you own, and the Two-Way Radio Reality Check does the same for GMRS talk time. Run the big load here; run the small ones there; and if the answer at both ends is “longer than the trip,” you can stop shopping and go.

Prices were checked on November 1, 2026 at each maker’s own store and move often; the buttons show the current Amazon price. Runtime figures use the 85% usable factor throughout — if a maker’s chart disagrees with this page, it is because the chart used the whole battery and a smaller load.