State of Health (SOH)

State of health (SOH) is a battery’s present capacity, and sometimes its internal resistance, expressed as a percentage of its value when new.

Cells lose capacity with every cycle and with time at high temperature or high state of charge. The battery management system tracks SOH and the energy management system uses it to size dispatch, to report degradation against the warranty curve, and to plan augmentation. A battery at 80 percent SOH holds 80 percent of its original energy but can usually still deliver its rated power.