A battery cartridge-connecting system for battery modules including bus bars, each of which includes a plate-shaped bar body, coupling parts, and electrical connection parts; a base plate, to which the bus bars are easily mounted; and a printed circuit board (PCB), which is easily coupled to the bus bars and is mounted to the base plate in a compact structure. The present invention also provides a battery module and a medium- or large-sized battery system including the battery cartridge-connecting system.