The battery for all 6x7 and 67 bodies is a tiny 6V 4LR44, available at electronics stores. Once in the clasp in the base of the camera, a 6-monthly check should be made to ensure there is no leakage. When the camera is not in use, even with film loaded, switch the shutter speed dial to B leaving the dial on any shutter speed with the shutter cocked will eventually make the shutter speeds quite inaccurate. A shutter that does not fire even with a fresh battery and film loaded has dead solenoids or circuit problems (the shutter and timing circuit itself is very rudimentary but calibrating speeds is a very specialised job).