A power supply apparatus includes a plurality of power storage modules that are connected in parallel and a backup power storage module that is connected in parallel with the plurality of power storage modules. When charging or discharging of at least one of the power storage modules is disabled, charging of the other power storage modules is inhibited, discharging of the backup power storage module is permitted, states of charge of the backup power storage module and the other power storage modules are detected, and charging of the backup power storage module and the other power storage modules is permitted in accordance with the detected states of charge.