Battery capacity calculator
A 100 Ah lead-acid battery holds 1,200 Wh on paper, but discharging it below 50% shortens its life dramatically — so the usable figure is 600 Wh. A 100 Ah lithium iron phosphate battery of the same nominal voltage will happily give 80 to 90%, so it delivers around 1,000 Wh. The lithium costs more per amp-hour and often less per usable watt-hour, which is the comparison that matters.
Watt-hours are amp-hours times nominal voltage. A 100 Ah 12 V battery holds 1,200 Wh, but only the usable fraction counts: 50% for lead-acid gives 600 Wh, while 80–90% for lithium gives 960–1,080 Wh from the same nameplate.
How to work out real battery capacity
Amp-hours alone tell you almost nothing, because the same 100 Ah means 1,200 Wh at 12 V and 4,800 Wh at 48 V. That is why higher system voltages are preferred for anything substantial — the same energy at a quarter of the current means thinner cable and lower losses. The second trap is that capacity ratings assume a slow discharge, typically over twenty hours. Pull the same battery hard and the Peukert effect means you get measurably less out of it, an effect that is pronounced in lead-acid and small in lithium.
Questions
Multiply amp-hours by nominal voltage. 100 Ah at 12 V is 1,200 Wh.