Fossil watches have an easy to open case back. You would want to open the case if you need to change the battery. All Fossil watches are quartz, meaning they are powered by a battery. You need a special watch opener tool to open the case back if you want to decrease the risk of scratching the case, otherwise you can use multipurpose tool to open the case.
Insert the watch case opener knife into the slit where the case back meets the case. If you do not want to purchase a watch case opener knife, you could use a tiny screwdriver to open the case, but be careful not to scratch the case with the screwdriver.
Carefully move the knife up and down to loosen the back of the case. Press down on the handle of the knife with force to pop the back of the case up.
Remove the rubber gasket from around the inside of the watch case. The rubber gasket ensures the case is waterproof. It is important to replace this gasket properly when you close the case.