Patent ID: 8855956

Claim:
A method of determining state of charge of an energy delivery device using a battery management system, comprising: sampling, by the battery management system, voltage values presented by the energy delivery device during a relaxation period of the energy delivery device; regressing at the battery management system, with respect to the sampled voltage values, (i) a first variable representing a real-time open circuit voltage value of the energy delivery device and (ii) a second variable representing a real-time overpotential value that describes a total overpotential being relaxed, wherein an equation used for regressing the open circuit voltage value and the overpotential value includes a time constant of relaxation, the time constant of relaxation being a fixed value that is (a) determined prior to the regressing and (b) determined as a function of the energy delivery device; and using a predetermined profile that relates open circuit voltage of the energy delivery device to state of charge of the energy delivery device, to determine a particular state of charge corresponding to the regressed open circuit voltage value.