Nest Thermostat Battery (Everything You Need to Know)

Okay, ladies and gentlemen, let’s talk about the batteries on your precious Google Nest Thermostats, shall we? Google Nest Thermostat units come with batteries. For the 1st, 2nd, 3rd gen Nest Learning thermostats, and even Nest Thermostat E, the battery is internal lithium-ion and charges quickly via a USB port when the level gets low. For Nest Thermostat, the battery is removable AAA alkaline batteries; these must be replaced when the unit sends a low battery warning.

About Nest Learning Thermostats internal battery

The internal battery in Nest Thermostats is lithium-ion. The thermostat units draw voltage from your heating and cooling wires to keep the internal battery charged.

In the event of a power outage or when you switch it off, the internal battery will have the capacity to keep the unit going for a while. The thermostat will also disconnect off the network and turn off the display to conserve battery and continue working for a while before it shuts down completely.

When the battery capacity gets low, you must charge the internal battery.

The following things cause Nest Thermostat battery capacity to get low:

  • A blackout event, as explained above.
  • Insufficient power in the heating and cooling wires.

How to check Nest Thermostat Battery Info

In case the battery is running below 3.6V, you will notice the thermostat switch off display and disconnect from wi-fi. You can confirm the battery level by checking the system settings. Here is how:

On your thermostat, navigate to the settings menu and click on <technical info>.

Check the Voc/Vin/Lin. The normal range for these specs should be as follows:

  • Voc: 29-42V
  • Vic: 28-42V if the system is shut down and 6-7V when running.
  • Lin: 20-40mA

If you have installed a C wire in the thermostat, the normal range for the specs should be as follows:

  • Voc: 29-42V
  • Vic: 28-42V
  • Lin: 100-200mA

If you find specs totally different from the above, try charging your thermostat.

How does a Nest Thermostat’s Internal Battery Charge?

Nest Thermostats internal battery can be recharged via the USB port located on the back of the units. Start by taking the display off the thermostat, then plug the thermostat into your computer USB or any other power source just like you always charge your phone. The unit will indicate it is charging by blinking red.

How long does the Nest Battery take to charge?

Usually, the internal lithium-ion in your Nest Thermostats takes just about half an hour to full charge. But it depends on how much the battery is drained.

It can take up to 2 hours to fully recharge the thermostat battery from a deficient battery level.

The following types of USBs are compatible with Nest Thermostat USB ports:

  • Micro-USB port for Nest Thermostat E, 2nd and 3rd gen Nest Learning Thermostats
  • Min-USB port for 1st gen Nest Learning Thermostat

For Nest Thermostat with removable AAA alkaline batteries, there is no USB port. Switch out old batteries for new fresh ones when the unit sends a low battery warning.

How long does the Nest Thermostat internal battery last without power?

As already mentioned, the thermostat charges the battery using the voltage in the connected wires. In the event of a power outage, it can keep working for a while, usually for about 60 to 120 minutes.

Keep in mind that the thermostat won’t be ‘smart’ anymore when running on low battery because it disconnects from wi-fi and switches off the display to conserve battery for a little longer. You will hear most people say the thermostat has become ?dumb’ because now, it can only be operated locally, not remotely. But once you recharge the battery , your Nest thermostat should resume ?smart’ operations without any issue.

Nest Thermostat is draining faster than it can charge?

If your Nest Thermostat battery is draining faster than it can charge, the following issues could be the cause:

  • Wi-fi
  • Defective display
  • Insufficient power in your system

You will notice the thermostat continuously blink red or green, or there won’t be any light at all. You’ll want to troubleshoot the unit immediately.

Fix #1: Disconnect from wi-fi

If your Nest Thermostat is constantly searching for a network to join, the battery is going to drain much faster. This is usually the problem when the wi-fi is out of range. But if your wi-fi signal is in range, the thermostat can easily connect to it without draining the battery too much; the battery only drains when the thermostat struggles to look for wi-fi.

To troubleshoot, disconnect from wi-fi and monitor; if the battery capacity starts picking up after disconnecting, your wi-fi is the issue:

  • Go to settings <reset> Network.
  • Reset all the network settings so the thermostat won’t try looking for wi-fi
  • Monitor battery charging status for a full day

Fix #2: Troubleshoot power wires

Sometimes, the thermostat battery may be draining fast because there is a problem with the connected wires such that the unit is not getting enough power.

The thermostats will display error codes N1, N21, N71, N2, N22, N72. N3, etc., to indicate an issue with the power wires. Here is how you can fix the error:

  • Cut off power to the thermostat at the system switch, the breaker box, or the fuse box.
  • Take the display off the unit.
  • Check if the connectors and wires are okay. Press down the connector button and insert the wires as far as they will go. If the button stays down when you release it, then the wires are correctly in place.
  • You may have to strip the wires to 1/3 or ? inch exposure.
  • Put the display back and turn the power back on.

Fix #3: Install a C-wire

The C-wire is a special power supply wire, so thermostats receive enough power always. It’s also called a common wire. However, most Nest brands don’t have C-wires; instead, they draw voltage from connected heating and cooling wires. The manufacturer says this is possible because the units aren’t power-hungry.

However, the voltage from the heating and cooling wires is not always consistent. You may notice strange heating and cooling behavior once you connect the thermostat. You may also notice the thermostat goes off when the display is connected. These issues can be corrected by installing a C-wire for a consistent power supply. Just ask for help from a local Nest Pro.

Nest Thermostat not charging?

Sometimes the Nest Thermostat battery won’t charge. This could have different causes:

Disconnected power wires

It may be due to disconnected power wires. As explained above, Troubleshoot and turn the power back on, which should fix the issue.

The power supply is cut off

Other times it’s because you haven’t turned on the power to the unit. Check that the fuse/ breaker switch is on. During installation, power is cut off from the thermostat to avoid blowing its fuse. The power should be turned on after the job is done.

The display is not positioned well on the base

Check that the display is seated correctly on the base. If not, the thermostat isn’t going to turn on and will not charge its lithium-ion battery.

Damaged thermostat

Reinstall an old thermostat to check if your setup is working as expected. If there is no problem when the old thermostat is on, your Nest Thermostat may be faulty and needs replacing.

Your batteries are spent

Another reason your thermostat is not charging could be because the batteries are bad and can no longer hold a charge. All lithium-ion batteries worsen with age, even though the manufacturer says they will last the ‘life’ of the product. If your batteries are failing due to age, consider replacing them.

How long will Nest thermostat batteries last?

In most cases, the internal lithium-ion battery lasts five years if used as the main power source. However, if used as a backup, it can last even longer.

The warranty on the batteries is 2 years for Nest Learning and a year for Nest E. However, if you get the thermostats and installation services from Nest Pro, you are up for an extended pro warranty.

In the case of battery issues, Nest’s advice is to seek the services of its trusted professionals. Don’t try removing the back cover of the thermostat. Tempering with the product in your DIY endeavors may cost you the warranty.

If your thermostat keeps dying even after troubleshooting the wi-fi, power supply, and display issue, you could do with a new battery. Contact your nearest local Nest pro for help.


Nest Thermostats come with batteries that are either internal or removable AAA alkaline cells. Internal batteries can be recharged faster via USB connection if the unit sends a red or green signal. When you plug the unit into a power source, it starts blinking red to indicate it is charging. However, in the case of a fast- draining battery or not charging, try the above fixes or contact a Nest pro for help.

Steven Carr

Steven is a certified IT professional and gaming enthusiast. He has been working in the tech industry for over 10 years, and specializes in all things Tech-related. When he's not geeking out over the latest hardware or software release, he can be found testing out the latest video game.

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