It is always best to have the battery in your watch replaced at regular intervals, except Eco-Drive watches, to reduce the risk of damage to the movement from leaking fluids from an expired battery. An expired battery has a greater chance of leaking fluids that could result in expensive repairs. If your battery expires while in the watch, have it replaced by qualified personnel as soon as possible. If your watch is water resistant, be sure to have the gaskets replaced and the watch water tested at the same time.