State of Charge (SOC)

State of charge (SOC) is the energy remaining in a battery expressed as a percentage of its usable capacity, with 100 percent full and 0 percent empty.

The battery management system estimates it from current counting corrected by cell voltage, and publishes it to the energy management system. SOC is the single input every dispatch decision depends on: how much can be discharged for a peak, how much room there is to absorb solar, and whether the battery can keep following a regulation signal. An EMS should range check every SOC reading and refuse to act on one outside zero to one hundred.