What does Nominal vs. Useable Capacity mean?

Explanation

Every EV battery has two capacity numbers. The nominal (or gross) capacity is the total energy the physical cells can store. The useable (or net) capacity is the portion the car allows you to access. The difference is a hidden buffer at the top and bottom of the battery that the BMS reserves to protect cell health and longevity.

For example, a car might have an 82 kWh nominal battery but only 77 kWh of useable capacity. The remaining 5 kWh is split between a top buffer (preventing the cells from reaching maximum voltage) and a bottom buffer (preventing them from being fully drained). When your car shows 0% SoC, there is still some energy in reserve.

This buffer is why you can sometimes drive a few kilometers after the car shows 0%. It is also why the advertised range is based on useable capacity, not nominal. When comparing battery sizes across brands, check whether the number is nominal or useable. Some manufacturers advertise the nominal figure (which looks bigger), while others show the useable figure (which is more honest).

Read more at National Renewable Energy Laboratory.

Where you'll see this

• In vehicle specifications

Common confusion

People sometimes think a 77 kWh battery from one brand is smaller than an 82 kWh battery from another, when in reality both might have the same useable capacity. Always compare useable capacity for accurate range comparisons.

Example

Related terms