Your Nest thermostat runs on two AA batteries that last about two years

The Nest thermostat uses two standard AA batteries as a backup power source. When the batteries run low, the thermostat displays a low-battery warning on its screen and sends a notification to your phone. You can replace them yourself in about two minutes without calling a technician or disconnecting anything from your wall.

The batteries keep your thermostat running if your power goes out. They do not power the thermostat during normal operation — that comes from your heating and cooling system's wiring. But if the power fails, the batteries let your thermostat keep its settings and continue to work until power returns.

Key Takeaways

  • Nest thermostats use two AA batteries that typically last two years before needing replacement.
  • You will see a low-battery warning on the thermostat screen or receive a phone notification when replacement is needed.
  • The entire replacement takes about two minutes and requires only two new AA batteries — no tools or technical knowledge needed.
  • Alkaline batteries work fine, but some owners report better longevity with lithium AA batteries in cold climates.

How to access and remove the old batteries

Start by looking at the back of your Nest thermostat. You will see a small slot or indentation near the bottom edge. This is the battery compartment cover. Gently push or slide this cover downward — the direction depends on your Nest model, but it will move with light pressure. The cover will pop out or slide free, revealing the battery chamber inside.

Inside the chamber, you will see two AA batteries sitting side by side. They are held loosely in place by the compartment itself, not by springs or clips. Carefully pull each battery straight out toward you. If a battery feels stuck, wiggle it gently side to side as you pull. Once both batteries are out, set them aside.

Installing the new batteries

Take your two new AA batteries and check the orientation markings inside the battery chamber. You will see a small diagram showing which end goes in first — usually the positive end (marked with a plus sign) faces outward. Insert the first battery into the left slot with the positive end facing out, then push it in until it sits flush. Repeat with the second battery in the right slot.

Once both batteries are seated, the thermostat may display a brief message or beep to confirm they are installed. This is normal. Slide or push the battery compartment cover back into place until it clicks or sits flush with the back of the thermostat. The low-battery warning should disappear from your screen within a few seconds.

What type of batteries to buy

Standard alkaline AA batteries work perfectly in Nest thermostats and are the cheapest option. Brands like Duracell, Energizer, or store-brand alkaline batteries all perform the same way. A two-pack costs between two and five dollars at any grocery store, pharmacy, or hardware store.

Some owners in very cold climates report that lithium AA batteries last longer — sometimes up to three years instead of two. Lithium batteries cost more per pair, usually between six and ten dollars, but may be worth it if you want to replace them less often. Both types are safe to use in your Nest thermostat.

When to replace the batteries

Your Nest thermostat will alert you when the batteries are running low. You will see a message on the thermostat display itself, and you will also receive a notification in the Google Home app on your phone. You do not need to replace them when ready — the thermostat will continue to work for several weeks after the warning appears.

However, it is a good idea to replace them within a week or two of seeing the warning. If your power goes out while the batteries are completely dead, your thermostat will lose its settings and stop working until power returns and the batteries are replaced. Replacing them promptly keeps your backup protection active.

Troubleshooting if the warning does not go away

If you have installed new batteries but the low-battery warning remains on your screen, first make sure both batteries are pushed all the way in until they sit flush. A battery that is not fully seated will not make proper contact. Remove each battery, look at the contacts inside the chamber to make sure they are clean and free of corrosion, then reinsert both batteries firmly.

If the warning still appears after reinserting the batteries, try removing both batteries and waiting thirty seconds before putting them back in. This can reset the battery sensor. If the warning persists after that, the sensor itself may be faulty — contact Google Nest support for a replacement unit, as this is a hardware issue rather than a battery problem.

How often you will need to replace them

Most owners replace the batteries once every two years. The exact timing depends on how often your power goes out in your area. If you live somewhere with frequent outages, the batteries will drain faster because the thermostat is using them more often. In areas with stable power, the batteries may last closer to three years.

You do not need to replace the batteries on a schedule — just wait for the low-battery warning. The thermostat will tell you when they are running low, so you do not have to guess or check them manually.

Frequently Asked Questions

Can I use rechargeable batteries in my Nest thermostat?

Rechargeable AA batteries work technically, but they are not recommended. Rechargeable batteries have a lower voltage than alkaline batteries and may not provide enough power to keep your thermostat running during an outage. Stick with alkaline or lithium batteries for reliable backup power.

What happens if I put the batteries in backwards?

If you insert a battery with the negative end facing out instead of the positive end, the thermostat straightforward will not recognize the batteries. The low-battery warning will remain on your screen. Remove the battery, flip it around, and reinsert it in the correct direction. No damage occurs from inserting a battery backwards.

Do I need to turn off my thermostat before replacing the batteries?

No. Your thermostat is powered by your heating and cooling system's wiring during normal operation, so removing the backup batteries does not interrupt anything. You can replace them while the thermostat is running without any issues.

Will my thermostat lose its settings if the batteries die?

Yes. If the power goes out and the backup batteries are completely dead, your thermostat will lose its temperature settings and schedule. When power returns, you will need to set up the thermostat again through the Google Home app. This is why replacing the batteries when you see the warning is important.

How do I know which end of the battery goes in first?

Look inside the battery chamber on the back of your thermostat. You will see a small diagram or markings showing the correct orientation. Usually the positive end (marked with a plus sign) faces outward toward you. If the diagram is hard to read, check the Nest support website or your thermostat's manual for a photo of the correct orientation.