Most watches operate using a small battery located inside the case back. These batteries eventually lose their power or may get wet if the watch is not waterproof. When this occurs, the watch no longer keeps time and the battery must be replaced. Replacing a watch battery can be fairly easy and generally only requires a few tools. The cost of replacing a watch battery can vary depending on watch type, battery type and if any tools are required. As of April 2010, the cost for most watch batteries is £3 and up, depending on the watch make and model.
Turn the watch over and look at the case back. If there are six small slots that are spaced equally around the case back, the watch is a screw back. Screw backs require a small tool to open. Try using a small pair of snipe nose pliers in the slots to loosen and open the case back.
Locate the small indention in the side of the case watch if there are no small slots, indicating that the watch is a screw back. Insert a small, flat tool such as the head of a standard screwdriver into the indention and slowly work it around the edge of the case watch, twisting gently as you go. The case back will snap off after it has been loosened sufficiently.
Look for the battery once the case back is off. It will look like a small, smooth disc. Some battery watches can be popped out by simply inserting a fingernail underneath the battery. Others are held in by a small clip. Pop open the clip and the battery will come out. Other batteries are held in the clip by a screw that can be removed with a small screwdriver. Set the screw aside once it is out and pop out the battery.
Set the new battery where the old battery was and replace the screw or clip if one is present.
Replace the case back by setting the watch face down on a slightly soft surface, such as a computer mouse pad. Line the small indention up on the case back with the indention in the side of the watch and then push down on the case back with both thumbs with even pressure. The cover should snap back into place.
Set the time on the watch, if necessary. Make sure the crown (the small knob on the right-hand side of the watch) is pushed in to the side of the watch fully after setting the time.
Place the watch in a warm place, such as the inside of a cupboard, overnight if the watch battery does not seem to be working. If this does not seem to solve the problem, take the watch to a jeweller for advice.
If you experience any difficulties removing or replacing the watch battery, take the watch to a jeweller or watch repair shop for assistance.