Power density
Power density is the amount of power per unit volume.
In energy transformers including batteries, fuel cells, motors, etc., and also power supply units or similar, power density refers to a volume. It is then also called volume power density, which is expressed as W/m3.
In reciprocating internal combustion engines, power density—power per swept volume or brake horsepower per cubic centimeter —is an important metric. This is based on the internal capacity of the engine, not its external size.Examples
| Storage material | Energy type | Specific power | Power density |
| Hydrogen | Stellar fusion | 0.00184 | 276.5 |
| Plutonium | Alpha decay | 1.94 | 38,360 |
| Supercapacitors | Capacitance | up to 15000 | Variable |
| Lithium-Ion | Chemical | ~250-350 | ~700 |
