Controller determines an output limit value that defines an upper limit of a current or power recommended for suppressing cell deterioration based on a voltage, a current, and a temperature of each cell, and notifies host controller in electric vehicle of the determined output limit value. When electric vehicle climbs a hill, controller calculates a current value or power value to be discharged from power storage unit, the current value or power value being required for electric vehicle to climb the hill at a speed not less than a set minimum speed, while suppressing an amount of deterioration of cells within an allowable range, and when the calculated current value or power value is larger than the output limit value, replaces the output limit value with the calculated current value or power value.