An embodiment contemplates a method of determining a state-of-charge of a battery for a vehicle. (a) An OCV is measured for a current vehicle ignition startup after ignition off for at least eight hours. (b) An SOCOCV is determined for the current vehicle ignition startup. (c) An SOCOCV—est is determined for a current vehicle ignition startup. (d) A determination is made whether the difference in the SOCOCV for the current startup and the SOCOCVest for the current startup is less than a predefined error bound using. Steps (a)-(d) is performed in response to the difference being greater than the predefined error; otherwise, determining an ignition-off current for the current vehicle ignition startup as a function of the SOCOCV of the current vehicle ignition startup and previous vehicle ignition startup, and a SOC based on current integration over time. Determining an SOCest of the current vehicle ignition startup using the processor.