Every power station is sold on its rated capacity in watt-hours (Wh): how much energy its battery cells hold. What you can actually draw from the outlets is less. Independent testers measure that usable capacity by running a steady load from full until the station shuts off, and it is the number to plan around.
Why usable capacity is lower
- The inverter. The battery stores direct current (DC); the wall-style outlets need alternating current (AC). Converting one to the other costs energy as heat, and the inverter’s own fans and electronics draw power the whole time it is on.
- The battery management system. To protect the cells, a station shuts down before they are truly empty.
- The load. Efficiency changes with how hard the station is working. Very light loads waste a larger share on the inverter’s own draw; very heavy loads add heat losses.
USB and 12 V outputs skip the inverter, so charging phones and laptops over USB-C usually gets you closer to the rated figure than plugging the same devices into an AC outlet.
What the tests show
Of the 121 power stations ranked here, 41 have at least one published independent capacity test. Across them, the median station delivered 85% of its rated capacity from its AC outlets. The best result was 96% (BLUETTI Elite 200 V2) and the worst 73% (Anker SOLIX F1500); 9 delivered less than 80%.
So for planning, a fair rule of thumb is to count on roughly 85% of the rated Wh when running AC appliances. A 1,000 Wh station running a 100 W load gives you about 8.5 hours, not 10.
How the rankings use it
Tested capacity is the second-heaviest factor in how we rank. Where tests exist, we also work out the price per usable watt-hour, which is fairer than price per rated watt-hour: a cheap station that delivers 75% can cost more per usable Wh than a pricier one that delivers 90%.
A station with no independent test gets a neutral score for that factor and is marked as estimated on its page. Each product page lists every test it uses, with a link to the source.
Quick answers
Is rated capacity a lie? No. It is the honest capacity of the cells. It just isn’t what comes out of the AC outlets.
Does a bigger station lose more? Not as a rule. Efficiency depends on the inverter design and the load, not on size.
Why do two tests of the same station disagree? Different loads, temperatures and test methods. We average every published test that states usable Wh or an efficiency figure.