Gather a small screwdriver, case knife or pry tool, tweezers, and the correct replacement battery
Place the watch face down on a soft cloth
Open the case back by removing screws or gently prying off the back
Note the battery type and orientation before removing it
Remove any battery clip or retainer if present
Lift out the old battery with tweezers
Insert the new battery in the same orientation
Reattach any battery clip or retainer
Check that the gasket is seated properly
Close the case back securely
Set the time and test the watch
Take the watch to a professional if the case is sealed or difficult to open