# Energy Density is expressed in Liters, Liters of What?

When looking at energy density of batteries it is often expressed as Wh/L. For instance, Wikipedia says Lithium Ion batteries have a density of 250–693 W·h/L. Liters is supposed to express the volume but the volume depends on the density of the substance. So liters of what? Water?

• "The volume depends on the density of the substance." This might be where the misunderstanding is coming from – electronpusher Jun 25 at 16:25

A liter is simply a unit of volume equal to 1000 cm$$^3$$. It could be a volume of anything (air, water, a solid). Technology is trying to pack more energy into a smaller volume of a battery to save space.