Calculator
Battery energy calculator
Pick a battery's voltage and enter its amp hours. You get its energy in watt hours, and how two packs compare.
In short
Energy in watt hours = nominal volts x amp hours, so an 18 V 5 Ah pack holds 90 Wh. A five-cell pack is sold as 18 V in the UK and 20 V max in the US: the same pack. Convert any max rating to nominal before you compare.
Compare two packs
Pack A against pack B
2.50 x the energy
- Lithium-ion cells are 3.6 V nominal and 4.0 V maximum, so "18 V" and "20 V max" packs are the same five-cell pack.
- Max ratings are converted to nominal before calculating: 12 V max is 10.8 V, 20 V max is 18 V, 40 V max is 36 V, 60 V max FlexVolt is 54 V (3 x 18 V).
- Runtime also depends on the tool and the load, so more watt hours means more work per charge, not a fixed number of minutes.
Common packs
| Pack | Nominal | Energy |
|---|---|---|
| 12 V max 2 Ah | 10.8 V | 21.6 Wh |
| 18 V (20 V max) 2 Ah | 18 V | 36 Wh |
| 18 V (20 V max) 5 Ah | 18 V | 90 Wh |
| 18 V (20 V max) 8 Ah | 18 V | 144 Wh |
| 36 V (40 V max) 4 Ah | 36 V | 144 Wh |
| 54 V FlexVolt 3 Ah | 54 V | 162 Wh |
10-cell packs: two strings of five in parallel, still 18 V, double the Ah. Wh = V x Ah.