Abstract: In a method for ascertaining the charge state of a battery based on its open circuit voltage which may be determined using various methods, the accuracy of the charge state calculation may be optimized if the error of the open circuit voltage, which would result from applying a first and at least one additional method for open circuit voltage determination, is calculated, and the charge state is ascertained based on the particular open circuit voltage, the error of which is smaller than the error, which would result from applying another method for determining the open circuit voltage.