Abstract: The internal resistance and state of health of a battery is measured at the same time in a short time by a simple method. A battery management device acquires a first difference between a voltage at a first start time point after an end time point when charging or discharging is ended and the voltage at a first time point when a first period elapses after the first start time point, further acquires a second difference between the voltage at a second start time point after the first time point and the voltage at a second time point when a second period elapses after the second start time point, estimates an internal resistance according to a relationship between the first difference and the internal resistance of the battery, and estimates a state of health according to a relationship between the second difference and the state of health of the battery.