To replace the call button batteries, follow the steps below;

1. Remove the name cover. (under the call button)
2. You will now see a rubber tip, remove it.
3. Then screw out the little screw. 
4. Using a screwdriver, pry open the bell via the underside.
5. Replace the CR-2032 battery.
6. Click the bell closed again.

The doorbell is ready to use again.