Gather a small screwdriver, case knife or watch back opener, tweezers, and a replacement battery
Work on a clean, well-lit surface
Identify the watch case back type
For a snap-back case, insert the case knife into the notch and gently pry it open
For a screw-back case, use the proper case opener and turn counterclockwise
For a watch with screws, remove the screws carefully and keep them safe
Note the battery model number before removing it
Remove the old battery with tweezers or a plastic tool
Avoid touching the movement or internal parts
Insert the new battery with the correct polarity
Make sure the battery sits securely in place
Check the gasket and replace it if damaged
Close the case back properly
Press the snap-back case closed evenly or screw the back on securely
Reinstall any screws if applicable
Set the time and date if needed
Check that the watch is running
Take the watch to a professional if it is water-resistant, sealed, or difficult to open