The Nest thermostat is fueled by the energy from your HVAC wiring and keeps its internal battery charged. The battery drains steadily over time, even while it is not in use. It will become unusable if the battery level falls below the minimum operational level. On the back of each Nest thermostat is a USB charging connector that may be used to manually charge the battery. Troubleshooting in general, and specifically troubleshooting the wiring between the HVAC and Nest depends on a variety of circumstances.The Nest thermostat’s internal rechargeable battery is represented by Battery Level. It ranges between 3.6 and 3.8 volts. Nest thermostats are powered by a Li-Ion battery pack with a voltage of 3.7 VDC (380 mAh). The battery charge is very low, but it is being charged, as indicated by a red light on the top of your thermostat’s display.

If you have a Nest thermostat in your home, you may have Nest low battery issues from time to time. The low battery could be caused by a variety of factors, and you’ll need to figure out what’s causing it. The low battery issue with the Nest thermostat can be resolved in a few ways.

In general, there are a few popular remedies for the low battery issue with the Nest:

It is necessary to charge the built-in battery.


When the battery voltage falls below the 3.8V minimum operating level, this method comes in handy.
Examine and correct any wiring issues between your Nest and your HVAC system.
If your Nest isn’t properly wired to your HVAC system, or if your HVAC system has third-party issues, the Nest won’t get enough power, and the battery will run out.
To power the Nest thermostat, you’ll need a C Wire Adapter.
Battery drain can occur if your HVAC system lacks a C wire, or if the C wire isn’t working properly, or if the wires that power the thermostat aren’t giving enough power. In this case, the low battery issues can be resolved by connecting the Nest to a separate C wire adaptor (24V transformer).

The energy from your HVAC wiring powers the Nest thermostat, which keeps its internal battery charged. If there is a blackout or your HVAC system is switched off for any other reason, the battery has enough capacity to keep running for a while. The thermostat will turn off some features, such as WIFI, in order to save battery life. If the battery continues to deplete, the thermostat will shut down completely.

Let me go over each of these tactics individually.

1. If your Nest Thermostat’s battery is low, charge it.

This method is typically utilized when your Nest thermostat has been stored in a box for a lengthy period of time. This is normal because the battery slowly depletes over time, even while not in use. If the battery level goes below the minimum operational level, it will become inoperable.

Another scenario is if your HVAC system has been turned off for an extended period of time. The HVAC system frequently powers the Nest thermostat, which also keeps the Nest battery charged. If the HVAC system is switched off, your Nest thermostat will turn off in a few hours due to battery drain.

A USB charging port is included on the back of each Nest thermostat and can be used to manually charge the battery.

How to charge a Nest thermostat’s battery:

Remove the Nest display and charge it via the USB connection on the back with a USB cord and a power charger (typical Android wall charger is fine). The USB cable should be either micro USB or small USB, depending on the model.
The battery should be charged for 2 to 3 hours.
Connect the display to the thermostat base and check the voltage using the Menu settings to make sure it’s 3.8V.

2. Look for any faults with the wiring between the HVAC and the Nest Thermostat.

Troubleshooting in general, and specifically troubleshooting the wiring between the HVAC and the Nest thermostat, is complicated by a number of factors, therefore it’s not appropriate to cover it in this post.

If I were to outline the main elements to look for when troubleshooting the wiring between the Nest thermostat and your system, they would be:

The first step is to ensure that your system and the Nest thermostat are both compatible. You may also use the compatibility checker to see if the Nest thermostat is compatible with your present system.
The Nest thermostat is usually powered by the HVAC system’s cabling. It is powered by the system’s wires for heating and cooling in some cases, but in others, a C wire is required to provide sufficient power in a consistent manner.
The type of cables used in troubleshooting is also important. This resource explains which wires are supported and which are not. A separate stand-alone power supply may be required for your Nest thermostat.
Consult a qualified electrician to determine the amount of electricity transmitted via the RC (red) and C (green) cables (blue). If you’re confident, you can do this with a voltmeter or multimeter. If you don’t already have one, I recommend the Fluke 107 AC/DC Current Handheld Digital Multimeter.
Check the fuses on your system’s control board. It’s possible that the Nest thermostat isn’t getting electricity because of a blown fuse.
Many sensors are used in some HVAC systems, making them extremely sensitive to changes in power, current, and other factors. You can contact a local Nest Professional to have your HVAC system’s wiring inspected and perhaps repaired.

3. Power the Nest Thermostat with a C Wire Adapter

This method is used when the problem of powering the Nest thermostat through the HVAC system cannot be overcome. When the C wire approach fails, the HVAC system does not provide sufficient power to the thermostat, or the thermostat and the HVAC system are simply incompatible, this method is utilized.

In this case, a Nest-compatible C Wire Adapter will serve.

Because of the great demand for this model, if it is not available, you may want to select the next model “HQRP 24V AC Adapter” with similar technical qualities.

The steps for using the C Wire Adapter are as follows:

At the circuit breaker, turn off the electricity.
The “C” terminal should be linked to any wire from your 24 volt adaptor, while the “RC” terminal should be attached to the other line. If the HVAC system has a cooling component, you may need to use the provided jumper to connect the “RH” and “RC” terminals.
Connect the wall outlet to the power adapter.
Turn the electricity on at the breaker.
The faceplate of your thermostat should be linked to it.
How can I see how much power my Nest thermostat has left?

Press the thermostat ring to bring up the Quick View Menu, then go to Settings > Technical Info > Power.

Look for the “Battery” number on the phone (it should be the first one).

If the voltage of the battery is 3.8V or higher, it is in good condition.

What do the Nest Thermostat’s battery levels mean?

Press the thermostat ring to bring up the Quick View menu. Then, from the drop-down menu, choose Settings > Technical Info > Power. Here are the figures for Battery Level, VOC, VIN, and IIN.

Battery Level represents the current voltage of the thermostat’s inbuilt rechargeable battery. It has a voltage range of 3.6 to 3.8 volts.

You’ll need 3.7V to install a software update.
The display requires 3.6V to turn on as you approach.
When the voltage goes below 3.6V, your thermostat will turn off Wi-Fi, delay software updates, and disable the screen to preserve the battery charge and prevent it from shutting down completely.

VOC, VIN, and IIN measure the electrical current that flows through your system’s connections to the Nest thermostat.

How long does the battery survive when the Nest Thermostat is turned off?

If your HVAC is turned off or if there is a power outage and there isn’t a continuous power source to the Nest thermostat, the battery can last one to two hours.

My Nest thermostat’s battery isn’t charging.

The battery in your Nest thermostat may not be charging for a variety of reasons. The best way to isolate the problem is to use a wall charger with an appropriate USB cable to charge the battery through the thermostat’s USB port on the rear.

Check the battery after 3 hours. If it’s charged, the problem is most likely the wiring between your HVAC system and the Nest thermostat.

If the battery does not charge after 3 hours or cannot be charged at all, it has most likely been drained below the minimum functional level and has gone into “sleep mode.”

You can seek a replacement from your provider if the battery is still under warranty; otherwise, you can try to jumpstart the Nest thermostat battery. This post will teach you how to revive Li-Ion batteries on your own.

What’s up with my Nest thermostat’s red blinking light?

A blinking red light on the top of your thermostat’s display indicates that the battery charge is very low, but it is being charged. There are different troubleshooting procedures to perform depending on when you see the red light. For further information, go to this page.

What type of battery does a Nest thermostat use?

A Lithium-Polymer battery pack with a voltage of 3.7 VDC powers the Nest thermostat (380 mAh).

If you need to replace the Nest battery, this battery pack is available on Amazon and is compatible with Nest learning thermostats (2nd and 3rd generation models) as well as other brands. When you click on the link, the entire list will appear in the product description field.