| watt-hour per kilogram | |
| Standard: | Unit accepted for use with SI |
| Quantity: | Specific energy |
| Symbol: | W⋅h/kg |
| Units1: | SI units |
| Inunits1: | 3600 J/kg |
The watt-hour per kilogram (SI symbol: W⋅h/kg) is a unit of specific energy commonly used to measure the density of energy in batteries and capacitors.
In the SI system of measurement, one watt-hour per kilogram is equal to 3600 joules per kilogram.
The batteries that Tesla uses in their electric cars deliver about 254 W⋅h/kg,[1] compared to supercapacitors that are typically rated between 3 and 10 W⋅h/kg,[2] with the best commercially available supercapacitors as high as 47 W⋅h/kg.[3]
Nuclear batteries based on betavoltaics can reach up to 3300 W⋅h/kg, although over much longer time periods.[4]