Smoke & CO alarms
Google Nest Nest Protect (Battery) 2nd gen battery
6 × 1.5V lithium primary cell
How to replace it
| How to open | Turn Protect counter-clockwise off the backplate. Open the battery door. Replace all six AA cells with Energizer Ultimate Lithium AA (L91), matching +/-. Close door (will not close until all six are in). Remount clockwise. Press the centre button twice to test. |
|---|---|
| Orientation | Match +/− markings in the compartment |
| Low battery indicator | Yellow night pulse and app/audio “battery is low” warning |
| Notes | Google Help: use Energizer Ultimate Lithium AA (L91) only for this procedure. Battery-powered Nest Protect uses six long-life lithium AA cells. |
| Access | Tool-free |
Important
- Not a sealed 10-year pack — uses six replaceable lithium AA (L91).
- Do not mix chemistries or leave empty slots; the door will not close until all six are installed.
- Alkaline AA is not the Google-specified chemistry for Nest Protect battery replacement.
Sources
Helpful for this device
Optional tools for opening, testing or charging — separate from the battery answer.
- Ansmann Energy Check LCD
Quick household cell check (good / low / replace)
- ZTS Mini-MBT Multi-Battery Tester
More informative state-of-charge style checks across common formats
- Battery tester
Quick good / low / dead check for household cells
New battery but still not working?
A fresh 6 × AA should restore Google Nest Nest Protect (Battery) 2nd gen if the battery was the problem. Work through the checks below before replacing the device.
- Check orientation
Confirm the cell is seated correctly: Match +/− markings in the compartment
- Check the battery type
This device needs 6 × AA (lithium_primary). Rechargeable cells are not supported for this device. Same size does not always mean the same battery.
- Check known model-specific issues
Not a sealed 10-year pack — uses six replaceable lithium AA (L91). Do not mix chemistries or leave empty slots; the door will not close until all six are installed. Alkaline AA is not the Google-specified chemistry for Nest Protect battery replacement.
- Confirm the battery itself
If you have a battery tester or multimeter, check the cell. A low open-circuit voltage often means replace; for rechargeable AA/AAA, a capacity test is more informative than voltage alone.
- Still not responding?
If a correct, fresh battery installed properly does not restore the device, the fault may be elsewhere — the device may need service or replacement.
Need to replace the device?
Google Nest Nest Protect (Battery) 2nd gen is still sold new. Only buy another if a fresh battery and the checks above did not help.