A storage battery device comprising: a plurality of storage battery cells (31-1 to 31-n) connected in series; a monitoring unit configured to measure voltages via terminals of the respective storage battery cells (31-1 to 31-n), and to obtain degradation information indicating degraded states of the plurality of storage battery cells (31-1 to 31-n) based on the voltages; a selection unit configured to select at least one cell from among the plurality of storage battery cells (31-1 to 31-n); a power supply unit configured to supply power to the storage battery cell (31-1 to 31-n) selected by the selection unit to charge the storage battery cell (31-1 to 31-n); and a control unit configured to switch, based on the degradation information obtained by the monitoring unit, a storage battery cell (31-1 to 31-n) to be selected by the selection unit, and to adjust the power supplied from the power supply unit, characterised by the storage battery device further comprising a storage unit configured to be supplied with power from and supply power to the storage battery cell (31-1 to 31-n) selected by the selection unit and configured to store the power, wherein the control unit is configured to switch, based on the degradation information, the storage battery cell (31-1 to 31-n) to be selected by the selection unit so that from among the plurality of storage battery cells (31-1 to 31-n), power can be supplied from a first storage battery cell to the storage unit and power can be supplied from the storage unit to a second storage battery cell in which capacity degradation is smaller than in the first storage battery cell. a plurality of storage battery cells (31-1 to 31-n) connected in series; a monitoring unit configured to measure voltages via terminals of the respective storage battery cells (31-1 to 31-n), and to obtain degradation information indicating degraded states of the plurality of storage battery cells (31-1 to 31-n) based on the voltages; a selection unit configured to select at least one cell from among the plurality of storage battery cells (31-1 to 31-n); a power supply unit configured to supply power to the storage battery cell (31-1 to 31-n) selected by the selection unit to charge the storage battery cell (31-1 to 31-n); and a control unit configured to switch, based on the degradation information obtained by the monitoring unit, a storage battery cell (31-1 to 31-n) to be selected by the selection unit, and to adjust the power supplied from the power supply unit, characterised by the storage battery device further comprising a storage unit configured to be supplied with power from and supply power to the storage battery cell (31-1 to 31-n) selected by the selection unit and configured to store the power, wherein the control unit is configured to switch, based on the degradation information, the storage battery cell (31-1 to 31-n) to be selected by the selection unit so that from among the plurality of storage battery cells (31-1 to 31-n), power can be supplied from a first storage battery cell to the storage unit and power can be supplied from the storage unit to a second storage battery cell in which capacity degradation is smaller than in the first storage battery cell.