Replacing a watch case back after changing the battery is usually a simple task, although most contemporary watches may need a watch press and a new gasket to press the case back flush against the case. Vintage watches from the 1970s, which was the first decade for battery-powered quartz watches, require few tools to secure the case back on to the case. Novice watch enthusiasts, who prefer to perform their own minor repairs, should take great caution in opening a case back. Consider having a trained watchmaker change the battery in a contemporary watch.
Clean the edges of the case and case back with a polishing cloth. Ensure the battery is snug in its holder. Following installation of the battery, do not touch the battery or movement, which is the electronic device that powers and regulates the watch.
Hold the watch face down between your fingers. Place the case back onto the case. Use one thumb to hold the case back down at 6 o'clock. Place the other thumb at 12 o'clock. Gently press the case back into the case. It should snap into place.
Inspect the case back to ensure it's flush against the case and the seam is tight.
Inspect the rubber gasket if your watch is equipped with one. Replace it if it appears old, brittle or split.
Place the watch face down in your hand. Place the gasket onto the case rim. Place the screw case back onto the case. Use a watchmaker's rubber ball, a balled up wad of duct tape or simply your fingers and rotate the case back clockwise until it's tight.
Tighten the case back securely, but not too tight that it could strip the threads of the case. Ensure the case back is flush against the case.
Place a piece of thick, soft cloth on the bed of a watch press. Place the watch face down on the cloth.
Place a new gasket on the case rim. Install a brass fitting into the top press holder. This fitting should fit to the edge of the case back but not beyond it.
Place the case back onto the gasket and case. Apply medium pressure of the press onto the case back until it snaps into place.
Place the watch case face down in your hand or on a clean, flat table. Place a new gasket on the case.
Use tweezers to pick up each screw (there are usually four) and place them in the holes.
Use a precision screwdriver to tighten the screws of the case back into the case. Tighten the screws evenly at alternate ends. For example, tighten the screw at 10 o'clock, and then apply the same pressure at 4 o'clock. Move to 8 o'clock, and then again to 2 o'clock until the case back is flush against the case.
Always replace the gasket even if the old one looks fine.
Never force anything. You will damage the watch.