A method and apparatus are provided for estimating a state of charge (SOC) of a battery. Curves are generated to expresses a relationship between a first parameter and an SOC over a region of interest. A voltage and a current of the battery during a period of time are measured to create a set of voltage and current data, which is then processed to create a set of processed data. The processed data is then combined with the generated curves to generate processed data as a function of SOC. A curve is generated that evaluates each SOC for accuracy and chance likelihood of fit. An SOC that minimizes both the error and chance is selected and output for display to the user on a user interface.