Before we talk about how to change the Nest battery, know that a single set can last the lifetime of the thermostat. That’s because batteries are only your backup plan–to be used in case of interrupted power flow from the C wire.
Battery power typically runs low only when the device is unable to draw adequate power from the HVAC systems. Or, if you don’t have a C wire, in which case you’ll probably see the Nest Note N260 error code.
Before changing the battery, you can try to recharge it with a USB Micro B cable port on the back of the thermostat. If that doesn’t work, here’s what to do:
Turn off the power at the main circuit before you work.
Pull away the thermostat from the wall and expose its back. You’ll see the battery panel held in place with screws.
Undo the screws to see the battery and circuit board.
Remove the old battery and insert the fresh set. You can order thermostat batteries on Amazon.
Replace the screws and reaffix the thermostat back on the wall.