Based on 40 years of watchmaking experience and according to a master watchmaker Mitchell Lodowski it highly recommended to have the battery inside your watch replaced every two years -2 Years. Over the years we have changed tens of thousands of watch batteries and we have noticed that customers who choose to wait till their watch stops are at a higher risk of battery acid leaking into the watch movement. Although a watch battery cell is miniature in size it is still composed on an Anode (-), a Cathode (+), an insulator, and a separator. Over a prolonged period of time, the separator degrades causing the electrolyte which is essentially a liquid containing ions of electricity to come in contact with the anode can cause a chemical decomposition which essentially leads to a watch battery leakage as seen on a picture below.