Changing your battery can be tricky so we would recommend that you ask a good quality jeweller to change your battery. Please remember to remind them to ensure the waterproof seal is maintained. Should you decide to change your own battery you can do so by carefully unscrewing the four screws on the back and removing the plastic gasket. Once you have replaced the battery, carefully fit the gasket and tighten the screws. You must ensure the gasket is correctly fitted and the screws are tightened to ensure a waterproof seal is achieved.