How to Charge a Nest Thermostat (All Models)

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Nest Thermostat Battery Won’t Charge – Fixes

Under normal circumstances, the Google Nest range of thermostats are pretty robust and solid pieces of kit, they just work with no fuss. However, problems can occur and one of the most frequent issues that users report is with the battery. More specifically, the battery won’t charge.

I’ll explain in detail how to charge a Nest Thermostat and fix the battery not charging. I’ll discuss any underlying problems that may be at the root of the problem, should it persist. 

Before I get into how to charge a Nest Thermostat battery, let’s first look at how to know if the battery is the actual issue.

How Do I Know the Battery is the Problem?

It may not be immediately obvious that the battery is the problem, battery issues can manifest themselves in a number of ways including.

  • The thermostat displays a battery error message
  • Sluggish response time, and jerky graphics and animations on the screen
  • Blinking red or green LED lights above the thermostat display
  • No Wi-Fi connection

The battery itself acts as a backup power supply for when there is a power outage or other power issue. It usually holds 3.8 volts of power, so when the charge drops below 3.6v, that’s when problems occur.

Of note, the basic Nest Thermostat model uses standard AAA batteries, so the Nest Thermostat battery won’t charge, it’ll need you to change the AAA batteries. While the Nest E and Nest Learning models use a built-in Lithium Ion battery, so the battery can be charged.

How to Manually Charge a Nest Thermostat

In this section I explain how to charge the battery, the process itself is simple and in most instances is all you will need to do to have your thermostat running smoothly again.

But if the problem reoccurs, there are a few steps and tests you can do to help diagnose the underlying problem, which I’ll also cover.

A Step-by-Step Guide to Manually Charge your Nest Thermostat

Hopefully a simple manual charge will fix whatever issues your Nest Battery is having. To charge your battery, follow the simple steps listed below. 

  1. Remove the Thermostat from its wall mounting. Simply grasp the outer edges and pull it away from the wall.
  2. Make sure the thermostat is turned off. Click the Thermostat to bring up the menu and using the outer ring find the Thermostat option and select it.
  3. Select the Off option and the thermostat should now be turned off. 
  4. On the bottom of the Thermostat, you will find a USB Socket. Depending on the model generation, it will either be a Mini-USB socket (1st Generation) or a Micro-USB socket (2nd Generation). You can use this port to charge your thermostat with a standard phone charger or by plugging it into your computer. 
  5. The Nest support pages recommend you charge it for 10 minutes with the power off, then remove it from the charger and switch the unit on before resuming charging.
  6. Once charging is resumed (still by cable) leave it charging until it has fully charged. This takes around an hour but in some instances can be longer. 
  7. Once charged, the Thermostat can be reattached to its wall housing base.

It is important to monitor the battery status once the unit is fully charged. If it still isn’t charging when attached to the wall, then further troubleshooting is required to diagnose the problem. 

How to Check Your Battery on a Nest Thermostat

As I noted earlier, a fully charged and healthy battery should be at 3.8 volts, when the voltage drops below its operating range is when problems occur.

Once you’ve manually charged your battery, if everything is okay, the battery should remain at this level. To check if this is the case follow the steps below.

  1. Enter the Nest Menu by clicking the Thermostat display face (which acts as a button)
  2. From here, twist the outer ring until you see the Settings option. Select this by clicking the thermostat.
  3. Navigate to and Select Technical Info 
  4. Select Battery and the level of charge should now be displayed
  5. If the Thermostat is online, you can also access the battery levels using the app

If the battery level remains at 3.8v then all is good, the issue is resolved.

However, if the battery level is falling, then it indicates that there is some kind of issue. It could be with the battery itself, but more commonly, it’s a power issue in your HVAC system, particularly if it’s a newer Thermostat.

There are a few steps you can take to attempt to diagnose the problem before calling a technician out, which I will list below.

But if it’s a brand-new Nest installation, you may want to check if there is a compatibility issue between your thermostat and your HVAC system. The Nest Support pages have a compatibility test that you can use to check. 

Troubleshooting Nest Battery Issues

Use the following steps to try to pinpoint the issue affecting your battery. 

  • Check the heating system power is on. Always start with the basics, it could be your heating system has been inadvertently switched off. 
  • Check the fuses to your heating system. 
  • Using a multimeter, check the wiring to the thermostat has power, there’s a RH, RC and probably a control wire. If you’re unsure about how to do this, then it may be time to call in a professional HVAC technician
  • If there isn’t a C-wire on your system then this may be the problem. Nest can supply an adapter that can be easily installed to rectify this. I will cover this in more detail below. 

Hopefully by now you have got to the bottom of your problem. If not then there is a very good chance that problem lies with your C-Wire, or lack of a C-wire, below are a few additional steps you can take. 

C-Wire Issues

The C-wire or common wire runs directly from your thermostat to your HVAC system. It is designed to provide constant power to your thermostat at 24 Volts AC. In many instances, the thermostat will not function without this wire. 

Important — Make sure your HVAC system is fully powered OFF before attempting any of these steps. If you aren’t comfortable wiring or accessing your Boiler, it’s time to call in a Pro

First, look at the HVAC system’s control board and see if there is wire attached to the C terminal.

If you have a C-Wire, then the first thing to do is to check both ends of the connection, i.e. at the thermostat and HVAC ends. Make sure it is attached to the C-terminal on the thermostat. If it already is attached, then make sure the wire is seated properly at both ends and is free from dirt or corrosion. 

If your HVAC system does haven’t a C-wire, you can install a C-wire or an “add-a-wire” accessory like this Venstar Add-A-Wire Kit on Amazon. It’s basically an adapter that’s installed to provide a 5th wire as your C-wire.

Unless you’re a professional HVAC technician yourself, it’s probably best to hire a professional technician to do the common wire installation for you. There is a full section on C-Wires and C-Wire and adapter installation on the Nest Support site. 

See these other troubleshooting articles for the Nest thermostat:

For more on Nest thermostats, see this comparison review article: ecobee vs. Nest Thermostats.

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Written by:

Greg Randall
Greg Randall is deeply immersed in Smart Home Technology, with years of experience in home automation, from smart displays to TVs. He enjoys sharing his passion and knowledge with like-minded enthusiasts. Beyond smart homes, Greg loves snowboarding and exploring new culinary scenes with friends, bringing a zest for adventure and fine dining to his tech-savvy lifestyle.