The Alarm.com ADC-VDBA-770BAT replaces existing ADC-VDB770 batteries that have reached end-of-life. The ADC-VDBA-770BAT can also replace the battery-less insert in the ADC-VDB770. Homes with a wired digital chime require a battery and cannot use the battery-less insert. If you are using a digital chime and purchasing a new ADC-VDB770, this is a required accessory, since they now ship with a battery-less insert.