Step 1. In some Casio watches (e.g. WVA-430 and G-100) the battery is held in place by a clip.
Step 2. To open this type of clip you will need a small screwdriver. Insert the screwdriver blade into the small hole at one end of the clip.
Step 3. Push the screwdriver away from the battery so that it lifts the end of the clip over the retainer. The clip will pop open.
Step 4. You can now slide the battery out from underneath the clip, replace with the new battery and simply push the clip back down to close.
