A backup power supply system (40, 40-1,40-N) comprising: a secondary battery; an interface unit configured to transmit a trigger signal based on an operation of a user; a charging and discharging control unit configured to perform control of discharging the secondary battery and then charging the secondary battery or control of charging the secondary battery and then discharging the secondary battery when the trigger signal is received from the interface unit; a detection unit configured to detect a voltage of the secondary battery at different timings; a remaining capacity estimating unit configured to estimate a remaining capacity of the secondary battery based on the voltage of the secondary battery; a deterioration estimating unit configured to estimate a deterioration state of the secondary battery based on the estimated remaining capacity; and a notification unit configured to notify the estimated deterioration state, characterized in that the charging and discharging control unit is configured to electrically isolate the secondary battery of the backup power supply system from a secondary battery of other backup power supply system (40-1,40-N) when the interface unit received an isolation request signal for requesting electrical isolation, and wherein the charging and discharging control unit is configured to charge or discharge the secondary battery of the backup power supply system (40,40-1,40-N) so as to have the same remaining capacity as the remaining capacity of the secondary battery of the other backup power supply system and then to electrically connect the secondary battery of the backup power supply system (40,40-1,40-N) to the secondary battery of the other backup power supply system (40,40-1,40-N) when the trigger signal is received from the interface unit instead of the isolation request signal and estimation of the deterioration state of the secondary battery of the backup power supply system (40,40-1,40-N) by the deterioration estimating unit is completed. a secondary battery; an interface unit configured to transmit a trigger signal based on an operation of a user; a charging and discharging control unit configured to perform control of discharging the secondary battery and then charging the secondary battery or control of charging the secondary battery and then discharging the secondary battery when the trigger signal is received from the interface unit; a detection unit configured to detect a voltage of the secondary battery at different timings; a remaining capacity estimating unit configured to estimate a remaining capacity of the secondary battery based on the voltage of the secondary battery; a deterioration estimating unit configured to estimate a deterioration state of the secondary battery based on the estimated remaining capacity; and a notification unit configured to notify the estimated deterioration state, characterized in that the charging and discharging control unit is configured to electrically isolate the secondary battery of the backup power supply system from a secondary battery of other backup power supply system (40-1,40-N) when the interface unit received an isolation request signal for requesting electrical isolation, and wherein the charging and discharging control unit is configured to charge or discharge the secondary battery of the backup power supply system (40,40-1,40-N) so as to have the same remaining capacity as the remaining capacity of the secondary battery of the other backup power supply system and then to electrically connect the secondary battery of the backup power supply system (40,40-1,40-N) to the secondary battery of the other backup power supply system (40,40-1,40-N) when the trigger signal is received from the interface unit instead of the isolation request signal and estimation of the deterioration state of the secondary battery of the backup power supply system (40,40-1,40-N) by the deterioration estimating unit is completed.