METHOD FOR DETERMINING STATE OF CHARGE OF A BATTERY BY MEASURING ITS OPEN CIRCUIT VOLTAGE

A method for determining the state of charge (SOC) of a battery by measuring its open circuit voltage (OCV) either with the battery in a fully rested state of chemical and electrical equilibrium or an active state during a period in which the battery settles after charge or discharge is stopped. A first type algorithm is developed to correlate the OCV in a fully rested condition (OCVREST) to the state of charge at which that measurement is taken. A second type algorithm is developed that predicts a final settling OCV of a battery (OCVPRED), based on the set of parameters of OCV, rate of change of OCV, and battery case temperature, acquired during the settling period of a battery not at rest. To determine the SOC of a battery being tested that is in the fully settled state the measured OCVREST is applied to the first type algorithm. To determine the SOC of a battery that has not fully settled, the data of the OCV, rate of change of OCV and battery temperature is applied to a second type algorithm to determine OCVPRED and the OCVPRED value is used in the first type algorithm to determine SOC.