While the Google Nest Protect (Wired) is powered by your home’s wiring, the backup batteries are required for safety in the event of a power outage in your home.
Nest Protect (Wired) requires 3 Energizer Ultimate Lithium (L91) AA batteries. These batteries are only used to set up Nest Protect and as a backup power source if there is a power outage in your home.
The backup batteries are included in the box and designed for a long life. If your home has a stable supply of power, the backup batteries should not need to be replaced (Wired), but if replacement is required Nest Protect will alert you.
How to tell if your batteries need to be replaced
If your backup batteries do get low, the Nest Protect light ring will pulse yellow and tell you to replace the batteries. You will also get a notification in the Nest app.
What happens to the green LED light if the power goes out?
The small green LED light on your Nest Protect (Wired) is required by regulation and lets you know that Nest Protect is receiving power. If the power goes out, the green LED will also go out.