Battery backup system

The invention provides a battery standby system, which comprises a battery pack, a charger, a discharger, a voltage detection and control circuit, a first protection switch, a second protection switch and a third protection switch, the battery pack is used for providing a standby power supply for a direct current bus, the charger is connected with the battery pack and used for receiving an external power supply, the discharger is provided with an input end and an output end, the input end is connected with the battery pack and the charger, the output end is connected with the direct current bus, the voltage detection and control circuit is used for detecting whether the voltage of the direct current bus is smaller than a first voltage drop point or a second voltage drop point, the first protection switch is connected between the battery pack and the input end of the discharger, the second protection switch is connected between the direct current bus and the output end of the discharger, the third protection s