Watt-hours are stored energy: the number of watts a battery could deliver for one hour. A load drawing 100 W for three hours consumes 300 Wh. It is the only capacity figure that compares two batteries of different voltages directly.
Capacity is where the specification sheets of this shelf diverge most, because the same battery can be described in three different units.
Energy against power
A watt is a rate — how fast energy is being used right now. A watt-hour is a quantity — how much there is to use. A kettle and a phone charger both draw power; only the kettle empties the battery quickly, because its rate is enormous.
Every runtime question is the same division: watt-hours available, divided by watts drawn, gives hours.
Why amp-hours mislead across voltages
Amp-hours count charge, not energy, so they only compare between batteries of the same voltage. An amp-hour at 12 V and an amp-hour at 24 V are not the same quantity of energy, and a table that mixes them is comparing nothing. Multiplying amp-hours by the nominal voltage gives watt-hours, and watt-hours compare freely.
Nominal against usable
The figure on the box is nominal. What comes out is less, for two reasons that stack: the chemistry is not discharged to zero, and converting stored direct current into mains-style alternating current costs something on the way out. Makers that publish a usable figure alongside the nominal one are making comparison easier, and this site reports both where both exist.
What the number never tells you
Watt-hours say nothing about age, temperature, or how many cycles the pack has left. A cold battery delivers less than the same battery warm, and a battery at the end of its cycle life delivers less than it did new — which is why the cycle rating always has a percentage attached to it.
Where this page and the manufacturer’s documentation differ, the documentation is the one to follow. Every capacity, output, input window, current limit, cycle count and temperature threshold on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And the distinction this page keeps: a nominal capacity is not the energy that reaches a socket. A reserve the chemistry never gives up, and the cost of converting stored direct current into a mains-style output, both sit between the two. Where a maker publishes a usable figure, this page reports it beside the nominal one; where only the nominal one exists, it says so rather than converting it.
What people ask before they order
How do I convert milliamp-hours to watt-hours?
Multiply amp-hours by the cell voltage. A bank sold in milliamp-hours nearly always counts them at cell voltage rather than at the voltage it outputs, which is why the two figures look so different.
Is a bigger watt-hour figure always better?
For runtime, yes. For usefulness, no: energy says nothing about how much power the battery can deliver at once, which is set by the inverter or the discharge limit.
Last reviewed 16 September 2026