Patent ID: 8452556

Claim:
A method of determining a state-of-charge for a battery, the method comprising the steps of: measuring open circuit voltages of a vehicle battery during ignition startups by a voltmeter; determining a startup state-of-charge of the battery by a control module as a function of a present open circuit voltage measurement for a present ignition startup, at least one open circuit voltage observation of a previous ignition startup, and a current draw integration over a time period from a previous ignition startup event to a present ignition startup event; determining a run state-of-charge change of the battery by the control module for an ignition key-on operation, the run state-of-charge change comprising a difference between the present open circuit voltage measurement and the at least one previous open circuit voltage observation, and determined in response to a current draw integration over a respective period of time; and calculating the state-of-charge of the battery by the control module based on a function of the startup state-of-charge and the run state-of-charge change of the battery.