This application provides a battery cell, a method and system for manufacturing same, a battery, and an electrical device. The battery cell includes: an electrode assembly; a shell assembly, configured to accommodate the electrode assembly and including a first side plate and a second side plate, where the first side plate and the second side plate are located on two sides of the electrode assembly along a first direction respectively; a pressure relief mechanism, disposed on the first side plate; and a support member, disposed between the electrode assembly and the first side plate, and configured to support the electrode assembly. A duct is provided on the support member. The duct is configured to guide gas between the second side plate and the support member into the pressure relief mechanism, so that the pressure relief mechanism is actuated to release a pressure when the pressure reaches a threshold.