What is battery energy density?

Two ways to measure it

Specific energy, also called gravimetric energy density, is the energy a battery holds per unit of mass, in watt-hours per kilogram (Wh/kg). Strictly speaking, energy density is energy per unit of volume, in watt-hours per liter (Wh/L), also called volumetric energy density. Both definitions appear in a December 2008 battery specifications guide from the MIT Electric Vehicle Team. Each depends on the battery's chemistry and packaging, the guide notes.

Why it matters

For electric vehicles (EVs), energy density helps determine how far a car can travel on a battery of a given size and weight. A battery with more energy in each liter can give a car more range from the same-size pack, the U.S. Department of Energy noted in April 2022. Or it can give the same range from a smaller, lighter and cheaper one, the department noted. It reported that the volumetric energy density of lithium-ion batteries rose from 55 Wh/L in 2008 to 450 Wh/L in 2020.

By weight, lithium-ion batteries reach up to 330 Wh/kg, according to an undated overview from the University of Washington's Clean Energy Institute. It puts lead-acid batteries at roughly 75 Wh/kg.

Where things stand in 2026

In its Global EV Outlook 2026, the International Energy Agency (IEA) gave these figures:

• Latest sodium-ion cells: up to 175 Wh/kg
• Newest lithium iron phosphate (LFP) batteries: up to 205 Wh/kg
• Lithium nickel manganese cobalt oxide (NMC) batteries: 265 Wh/kg

NMC's higher figure has not made it the most widely used chemistry. LFP accounted for more than 55% of EV batteries deployed worldwide in 2025, the IEA said. LFP packs were on average more than 40% cheaper per kilowatt-hour than NMC packs that year. But the agency said part of that gap reflects stationary storage, which mostly uses LFP and has lower energy density requirements. Packaging also counts. Cell-to-pack designs, which remove the modules between cells and pack, raise overall energy density, the agency noted.

Research targets sit higher. The Battery500 Consortium, formed in 2016, is led by Pacific Northwest National Laboratory. The consortium lists a goal of up to 500 Wh/kg with 1,000 charge and discharge cycles, using lithium-metal anodes. Solid-state batteries, which use a solid electrolyte, have drawn investment on the promise of longer range and better safety. But the IEA said those gains had yet to be shown in real-world use.