Battery state-of-charge estimation apparatus

A battery state-of-charge estimation apparatus comprising:

• a storage unit that stores a charge SOC-OCV curve indicating a correlation between a state of charge and open-circuit voltage of a battery, a discharge SOC-OCV curve different from the charge SOC-OCV curve and indicating the correlation between the state of charge and the open-circuit voltage, and internal-division-ratio information indicating a correlation between an internal division ratio achieved when a line between the charge SOC-OCV curve and the discharge SOC-OCV curve is internally divided at a predetermined internally dividing point and a battery capacity difference between the battery before charging or discharging and the battery after charging or discharging;
• and
• a state-of-charge estimation unit that, when the capacity difference is equal to or greater than a threshold, estimates, by referring to the charge SOC-OCV curve or the discharge SOC-OCV curve, that a state of charge, that corresponds to the open-circuit voltage is the state of charge of the battery, and that, when the capacity difference is less than the threshold, refers to the internal-division-ratio information so as to determine an internal division ratio that corresponds to the capacity difference, and estimates the state of charge of the battery by using the determined internal division ratio, the open-circuit voltage, the charge SOC-OCV curve, and the discharge SOC-OCV curve.