Power Density
Power density is the rate at which a battery can deliver or accept power relative to its volume, normally expressed in watts per liter (W/L).
Related power measures
Specific power is the corresponding mass-based measure, expressed in watts per kilogram (W/kg). The terms are sometimes used loosely, but they are not interchangeable: power density answers how much power fits into a given volume, while specific power answers how much power is available for a given mass.
Neither measure is the battery's total power. A large pack with moderate power density can deliver more kilowatts than a small pack with a higher density. Cell-level, module-level, and pack-level values must also be compared on the same basis because cooling, structure, connections, and controls add volume and mass.
Power figures need a duration and operating conditions. Peak output may be available only briefly, while continuous power must remain within voltage, current, and thermal limits. Temperature, state of charge, cell chemistry, cooling, and aging can all change the available result. State of Power (SoP) describes the battery management system's current estimate rather than a fixed material or design metric.
For chemistry and the trade-off between power and Gravimetric and Volumetric Energy Density, see Battery Cell Chemistry.