Storage for storing a plurality of used battery units, comprising: a memory unit that stores a predetermined SOC (State of Charge) range according to characteristics of each of the plurality of used battery units; a connection circuit that electrically connects the plurality of used battery units with each other; a recognition unit which is connected to the plurality of used battery units in storage and which recognizes a current value and a voltage value of each thereof; a selection unit that selects a discharge target battery unit to be discharged and a charge target battery unit to be charged from among the plurality of used battery units based ono a recognition result by the recognition unit and the predetermined SOC range of each of the plurality of used battery units stored in the memory unit; and a charge/discharge control unit which causes the discharge target battery unit to be discharged and the discharged power to be charged into the charge target battery unit such that the SOCs of the discharge target battery unit and the charge target battery unit reach the predetermined SOC range, characterized in that the storage for used battery units includes further: a charge unit which is electrically connected to the connection circuit and charges the plurality of used battery units, wherein the selection unit is configured to select the charge unit as a power source supplying power that covers insufficient power in a case where an amount of power discharged from the discharge target battery unit is insufficient for an amount of power required to charge the charge target battery unit to the predetermined SOC range, and the charge/discharge control unit is configured to cause the discharge target battery unit to be discharged or the charge unit to be discharged, and to charge the discharged power into the charge target battery unit such that the SOCs of the discharge target battery unit and the charge target battery unit reach the predetermined SOC range. a memory unit that stores a predetermined SOC (State of Charge) range according to characteristics of each of the plurality of used battery units; a connection circuit that electrically connects the plurality of used battery units with each other; a recognition unit which is connected to the plurality of used battery units in storage and which recognizes a current value and a voltage value of each thereof; a selection unit that selects a discharge target battery unit to be discharged and a charge target battery unit to be charged from among the plurality of used battery units based ono a recognition result by the recognition unit and the predetermined SOC range of each of the plurality of used battery units stored in the memory unit; and a charge/discharge control unit which causes the discharge target battery unit to be discharged and the discharged power to be charged into the charge target battery unit such that the SOCs of the discharge target battery unit and the charge target battery unit reach the predetermined SOC range, characterized in that the storage for used battery units includes further: a charge unit which is electrically connected to the connection circuit and charges the plurality of used battery units, wherein the selection unit is configured to select the charge unit as a power source supplying power that covers insufficient power in a case where an amount of power discharged from the discharge target battery unit is insufficient for an amount of power required to charge the charge target battery unit to the predetermined SOC range, and the charge/discharge control unit is configured to cause the discharge target battery unit to be discharged or the charge unit to be discharged, and to charge the discharged power into the charge target battery unit such that the SOCs of the discharge target battery unit and the charge target battery unit reach the predetermined SOC range. a charge unit which is electrically connected to the connection circuit and charges the plurality of used battery units, wherein the selection unit is configured to select the charge unit as a power source supplying power that covers insufficient power in a case where an amount of power discharged from the discharge target battery unit is insufficient for an amount of power required to charge the charge target battery unit to the predetermined SOC range, and the charge/discharge control unit is configured to cause the discharge target battery unit to be discharged or the charge unit to be discharged, and to charge the discharged power into the charge target battery unit such that the SOCs of the discharge target battery unit and the charge target battery unit reach the predetermined SOC range.