The pendant battery is a 23A 12V battery available at most supermarkets. We state that they should be replaced every 2-3 years, they will however continue many more years in most instances. You can press the yellow centre button (Local Nurse Call Button) on the pendant and you will see a blue light flash on the pendant and also hear a loud door bell chime coming over the loud speaker of the dialler indicating that your battery is communicating Ok with the dialler.