An unwelded battery assembly (32) is fed to a shuttle (36) which moves the unwelded battery assembly (32) to a moveable platform (46) in a raised position. The platform lowers the battery assembly into a nest (44) which rigidly supports the battery assembly. An ultrasonic horn is lowered into contact with the battery assembly and welds the battery cover (16) to the battery housing (14). The welded battery assembly (57) is then raised out of the nest by the moveable platform (46), and is moved to a second stage (48) while another unwelded battery assembly is shuttled to the platform. A central control circuit (49) operates and synchronizes the apparatus.