The life of a watch battery depends on a number of factors. It's easy to forget that our favorite wearable time-tellers have numerous tiny parts that work daily to keep us on an accurate schedule. These parts are all lubricated to reduce the friction and ultimately the energy it takes to make them run. A brand-new watch, with freshly lubricated gears, takes the least power to run and therefore the battery can potentially last a few years. As a watch ages, the lubricants dry which causes more energy to be used to power the gears. The average length of time a battery will last in a typical watch is approximately one year. If you need a battery change more frequently than once per year, it may be time to have your watch serviced; during a watch servicing the movement is cleaned of old lubricant, etc. and re-oiled.