Ah to kWh: multiply by the battery voltage
Multiply by the battery voltage, not by the mains voltage. A table for 100, 200 and 314 Ah at 12, 24 and 48 V, plus the mistake people make most often.
A 100 Ah battery at 12 V holds 1.2 kWh. The formula is short: amp-hours times volts, divided by a thousand.
The usual mistake comes from putting in the wrong voltage. People reach for 230 V because that is what comes out of the wall, and end up with 23 kWh instead of 1.2 kWh — nineteen times too much. The battery has its own voltage and that is the one that counts. Mains voltage appears on the far side of the inverter, and it changes the form of the energy, not the amount.
The same cells in a different arrangement give a different number. Four 100 Ah batteries in series are still 100 Ah, but at 48 V, so 4.8 kWh. Wire them in parallel instead and you get 400 Ah at 12 V — and exactly the same kilowatt-hours.
Common capacities
| Capacity | At 12 V | At 24 V | At 48 V |
|---|---|---|---|
| 100 Ah | 1.2 kWh | 2.4 kWh | 4.8 kWh |
| 200 Ah | 2.4 kWh | 4.8 kWh | 9.6 kWh |
| 230 Ah | 2.76 kWh | 5.52 kWh | 11.04 kWh |
| 280 Ah | 3.36 kWh | 6.72 kWh | 13.44 kWh |
| 314 Ah | 3.77 kWh | 7.54 kWh | 15.07 kWh |
Where 280 and 314 Ah come from
Those are the capacities of single prismatic LiFePO4 cells, the building blocks of most home storage banks. Four of them make 12 V, sixteen make 48 V. That is why these two odd numbers turn up in listings more often than round hundreds.