A reverse-connection protecting device comprises an interface, a battery control module and an activation module. The interface includes first and second lead-in ends coupled to respective ones of first and second lead-out ends. The second lead-in end is couplable to a negative terminal of a backup battery. The second lead-out end is couplable to each negative terminal of a load and an external power supply. The battery control module is coupled to the first lead-in end of the interface and couplable to a positive terminal of the backup battery. The battery control module is configured to control the charging or discharging of the backup battery. The activation module is coupled to the battery control module, and couplable to the load and the external power supply. The activation module is configured to drive the battery control module after the external power supply is powered on, but disable the battery control module in an instance in which the load, the backup battery or the external power supply is reversely connected.