Gather a small flat tool, case knife, or precision screwdriver
Place the watch face down on a soft cloth
Identify the case back type: snap-off, screw-down, or screwed
For a snap-off back, insert the tool into the notch and gently pry it open
For a screw-down back, use a case opener or rubber ball to turn it counterclockwise
For a screwed back, remove the screws with the correct small screwdriver
Locate the battery and note its position
Release any battery clip or retainer if present
Lift the battery out with plastic tweezers or a non-metal tool
Avoid touching other components
Insert the new battery with the same orientation
Reattach any battery clip or retainer
Close the case back securely
Check that the watch is running properly