What do the watts and watt-hours on a power station actually mean?
Power basics Updated 2026-08-01
A power station has two headline numbers and they answer two different questions. Watts (W) are the ceiling on what you can switch on at one moment — a 1,500 W heater needs a machine rated above 1,500 W or it will not run at all. Watt-hours (Wh) are how much energy is in the battery, which is what decides how long anything runs.
There is a third number, and it is the one that matters most: usable watt-hours. The nameplate watt-hour figure is the cell pack; what reaches your appliance is less, because the battery is not discharged to empty and the inverter loses some of it as heat. On this site only that third figure is ever divided by a load.
The two numbers, on one real machine
BLUETTI Elite 200 V2 — the three quantities
These are the record as published, not a worked example. The third row is computed from the first two coefficients the brand states, which is why its confidence is capped below the specs around it.
The ceiling on simultaneous load. Nothing about the battery is involved in this number.
See the record →The nameplate. Marketing quotes this one; nothing divides it.
2,073.6 Wh nameplate × 90% depth of discharge × 85% inverter efficiency = 1,586.3 Wh
What is left after the depth of discharge and inverter efficiency this brand publishes. This is the only figure a runtime may be divided out of.
Computed rather than published: the brand states the coefficients and not the figure, which is why the row is stamped as derived and its confidence sits below the two above it.
officialverified 2026-08-01BLUETTI Elite 200 V2 · US record
The gap between the second and third rows is not rounding. It is the part of the pack that is never delivered plus the part the inverter turns into heat, and on portable hardware the two together are commonly a fifth to a third of the nameplate. Any page that divides a nameplate watt-hour rating by an appliance wattage produces a confident-looking number that is wrong in one direction only: too long.
What a runtime division actually looks like
BLUETTI Elite 200 V2 running full-size refrigerator
The same division the runtime calculator performs, with every term shown. Note the denominator: it is the load plus what the machine itself consumes just being switched on.
The usable-capacity figure above, after the efficiency treatment its basis calls for.
The appliance's own average draw across its cycle — the duty-cycle article explains why this is below its running watts.
See the load record →The station's own self-consumption. Brands that do not publish it make every runtime on the internet optimistic by this much.
Usable energy divided by the two draws above. Computed on this build by the same engine the calculator runs.
See the full working →officialverified 2026-08-01BLUETTI Elite 200 V2 × full-size refrigerator
Change the load and only the denominator moves. The same machine holding 1,500 W of resistive heating runs for 1.1 h — the battery has not changed, the appliance has. That is the whole reason "how long does a power station last" has no answer without naming the load.
Why most of our records refuse to give you hours
Of the 29 station records in this library, 6 publish enough to support an hour figure. The rest state a nameplate watt-hour rating and nothing about depth of discharge or inverter efficiency, so there is no defensible usable-capacity number for them — and those pages print no runtimes at all. They show the load’s energy rate in watt-hours per hour instead, which needs no battery figure and is the number you actually size against.