The energy density of batteries can be displayed in two different ways: gravimetric energy density and volumetric energy density.
The gravimetric energy density is the measure of how much energy a battery contains in proportion to its weight. This measurement is typically presented in Watt-hours per kilogram (W-hr / kg). The volumetric energy density, on the other hand, is compared to its volume and is usually expressed in watt-hours per liter (W-hr / L). Generally, we refer to battery energy density as gravimetric ( weight ) energy density, and watt-hour is a measure of electrical energy, equivalent to one hour, one watt of consumption.
In contrast, the power density of a battery is a measure of how fast energy can be delivered, not how much stored energy is available. Energy density is often confused with power density, so it is important to understand the difference between the two.