Backup power supply system, moving body, control method for backup power supply system, and program

A backup power supply system (1) is provided with a first terminal (T1), a second terminal (T2), a disconnection unit (10), a current detection unit (20), a charging/discharging unit (30), an auxiliary power supply (40), and a control unit (50). The disconnection section (10) is connected between a first terminal (T1) to which the main power source (2) is connected and a second terminal (T2) to which the load (3) is connected. The charging/discharging unit (30) is connected between the auxiliary power supply (40) and a node (P1) between the disconnection unit (10) and the second terminal (T2). In a non-failure state in which the main power source (2) does not fail, the charging/discharging unit (30) receives power supply from the main power source (2) and causes a charging current to flow to the auxiliary power source (40), and in a failure state, receives power supply from the auxiliary power source (40) and causes a discharging current to flow to the load (3). The control unit (50) controls the disconnectio