Patent ID: 7075305

Claim:
A method for judging the condition of a secondary battery by applying an AC voltage to the secondary battery to detect a) a quantity of electricity, which is related to an impedance of the secondary battery, and b) a quantity of electricity, which is related to the maximum power density, and judging the performance of the secondary battery based on the detected quantity of electricity, comprising the steps of: obtaining a quantity of electricity related to the component of the impedance of the secondary battery, which does not vary with the frequency component of the AC voltage, as a DC impedance related quantity of electricity; obtaining the quantity of electricity related to the component of the impedance of the secondary battery, which varies with the frequency component of the AC voltage, as an AC impedance related quantity of electricity; and determining the secondary battery is good when both said DC impedance related quantity of electricity and said AC impedance related quantity of electricity are respectively predetermined values or less while determining the secondary battery is inferior when both said DC impedance related quantity of electricity and said AC impedance related quantity of electricity are respectively more than predetermined values.