Secondary battery state-of-charge estimating device and secondary battery state-of-charge estimating method

A secondary battery state-of-charge estimating device comprising:

• a detector configured to detect a charge/discharge current and a voltage between terminals of a secondary battery;
• a current-integration SOC calculator configured to calculate a state-of-charge value of the secondary battery based on a detection result of the detector by a current integration method;
• a state estimation SOC calculator configured to calculate a state-of-charge value of the secondary battery based on a detection result of the detector by a state estimation method;
• a convergence determiner configured to determine convergence of state estimation by the state estimation SOC calculator;
• and
• an SOC selector configured to select a state-of-charge of the secondary battery from the state-of-charge value calculated by the current-integration SOC calculator and the state-of-charge value calculated by the state estimation SOC calculator, according to a determination result of the convergence determiner,
• wherein the convergence determiner determines as the state estimation is non-convergent when the convergence determiner determines that the secondary battery is being charged and change of a given charging parameter is smaller than a given threshold.