State of Charge (SoC)
State of charge (SoC) is an estimate of how much of an EV battery's usable energy remains, usually shown as a percentage. It is the battery equivalent of a fuel gauge, but it is calculated rather than measured directly as a liquid level.
How to read it
The battery-management system estimates SoC from voltage, current, temperature, and a model of the battery's behavior. The estimate can be refined as the vehicle charges, rests, or operates. A displayed 0% and 100% normally represent the limits made available by the vehicle, not necessarily the cells' absolute electrochemical endpoints.
SoC is not the same as remaining range. Two vehicles at 50% can have different energy available, and the range estimate also responds to consumption, speed, weather, elevation, and cabin-climate use. For battery terminology and usable capacity, see EV Battery Basics; for monitoring and estimation, see Battery Management System.