Garmin Forerunner fitness watches fit snuggly around the wrist and keep track of your heart rate, pace and calories burnt while exercising. Garmin Forerunner's are embedded with a GPS that allows you to use the fitness watch on open land, heavily wooded areas and in cities with large high-rise buildings. Garmin offers over seven different types of Forerunner fitness watches that range from £97 on up, as of 2010.
Lay the Garmin Forerunner on a flat surface, watch face down. Because the inside components of the watch are quite small, you may want to use a magnifying glass while you work. Work in a well lit area.
Remove the four screws on the Forerunner backing with your Phillips head screwdriver. Set the screws aside. A magnetic screwdriver will stop the screws from rolling away.
Lift away the watch backing and set aside. Gently peel away the white sticker to expose a spring clip.
Remove the spring clip by inserting the small flathead screwdriver into the hole between the spring clip and the watches metal casing. Push down and the spring clip will pop off.
Remove the circular piece of white plastic with your tweezers and set aside. Remove the old lithium battery and replace with a new one.
Replace the white, plastic circle, then the spring clip. Insert the small end of the spring clip first and then the wider end. Push down to secure. Replace the white sticker and the watch backing. Insert the screws into place and tighten with your screwdriver to finish.