Patent ID: 8078416

Claim:
A method for estimating a remaining electrical charge or a remaining capacity of a battery that supplies power to a load, the method comprising: using, at a controller of a battery system, an approximate exponential decay function including a plurality of exponential function terms of time and a plurality of coefficients; stopping, at the battery system, a charge or discharge operation of the battery for a predetermined time; measuring, at a sensor of the battery system, a voltage of the battery at a plurality of instances during the predetermined time; obtaining, at the controller of the battery system, a relationship between the voltage of the battery and time; determining, at the controller of the battery system, the coefficients based on the obtained relationship between the voltage of the battery and the time, wherein the determining includes determining at least one power coefficient of an inferior logarithm of the exponential function terms by expressing the at least one power coefficient of the inferior logarithm of the exponential function terms as a predetermined function of temperature; and obtaining, at the controller of the battery system, an estimate of a stable open circuit voltage of the battery based on determined values for the coefficients.