A battery box includes a box body composed of a housing and a lid. The box body has two opposite lateral sides provided respectively with a joining mechanism and a locking mechanism. A power source assembly is received in the box body and includes a circuit board, a power supply unit, and an external-connection cable. The joining mechanism allows the lid to be connected to the housing in a detachable and rotatable manner. The battery box can be switched to an operation mode that allows connection to an external power source device so as to adapt to modern application environments and provide more, and more convenient, operation modes.