Gather a small screwdriver or case knife, tweezers, a replacement battery, and a clean cloth
Place the watch face down on a soft surface
Open the case back by removing screws or prying off the back, depending on the watch type
Locate the battery inside the watch
Note the battery model number and orientation
Remove any battery clip or retaining cover if present
Lift out the old battery with tweezers or a non-metal tool
Insert the new battery in the same orientation
Reattach any battery clip or retaining cover
Check that the gasket is seated properly if the watch is water-resistant
Close the case back securely
Test the watch to confirm it is working
Reset the time and date if needed