Updated April 15, 2024

Changing HVAC thermostat batteries is one of those tasks you usually only do once the batteries die. Yet, it only takes a few minutes, one or two new batteries, and a flat-head screwdriver if any tools are needed.

Here we’ll share how you can tell when the batteries are low, how to change them in three common thermostats, reasons the new batteries could quickly drain out, and what happens if you ignore the low battery messages.

How to Tell Thermostat Batteries are Low

Nearly all programmable and digital thermostats have a low battery indicator.

The next time you glance at the display for the indoor temperature, give it a second look for an indicator, such as:
  • A battery symbol,
  • A flashing light, or
  • A low-battery text message.

Most thermostats give a warning at least one month, if not two, before the batteries fully drain. But, if you see a blank display, the batteries have died and should be replaced as soon as possible.

What Kind of Batteries Does My Thermostat Need?

It depends on your thermostat, though the owner’s manual should say what type of battery and how many you’ll need.

Commonly used batteries include:
  • Two AA or AAA 1.5V alkaline batteries;
  • One button-style 3V lithium battery; or
  • One 9-volt battery.

HVAC thermostats hardwired into the home or business’s electrical system may or may not have a backup battery. Check the owner’s manual for your system to find out.

How to Change a Wall Thermostat Battery

Most digital and programmable wall thermostats allow for easy battery replacement.

Along with a small flat-head screwdriver, you may need a flashlight for better visual acuity.
  1. Depending on your thermostat, you’ll either slide the display cover upward and then pull it toward you or pull it straight off the wall mount.
  2. Locate the batteries inside the thermostat, then use a flat-head screwdriver to lift the batteries from the housing gently.
  3. Insert the new battery and check that the battery ends align with the correct terminal before installing.
  4. Push the display cover back into the wall mount, or slide it down until it clicks into place.

How to Change a Honeywell Thermostat Battery

Many Honeywell brand thermostats have built-in tabs to make changing the batteries tool-free.
  1. To remove the battery compartment, look for a tab on the top right side. Push the tab, then pull it toward you; the compartment should easily slide out.
  2. Remove and replace both AAA batteries — new batteries have a longer functional lifespan and provide even power to the thermostat.
  3. Insert the compartment into the display bottom-first, then slide until it snaps.

Your Honeywell thermostat display should light up as it powers on within a few seconds.

How to Change a Nest Thermostat Battery

    Check which version of the Nest thermostat your home or business uses. Nest E and Nest Learning thermostats don’t use physical batteries and must be recharged via a USB cable.

  1. Gently pull the display toward you to remove the thermostat from the base.
  2. Extricate the batteries from the back of the thermostat and throw them away.
  3. Insert two new batteries, checking that the positive and negative ends are aligned with the terminals.
  4. Push the display onto the base until it clicks into place.

When Should I Change My Thermostat Batteries?

Ideally, once a year, even if the battery manufacturer claims the batteries last longer. Many home and business owners change them during a seasonal tune-up. Plus, if your home or business uses carbon monoxide detectors, it’s recommended to change these batteries simultaneously.

What Happens if I Don’t Change the Thermostat Battery?

  • The thermostat display goes blank: When this happens, you won’t be able to change any settings, and any settings you’d programmed are lost.
  • The HVAC system operates erratically: Because the thermostat tells the entire system how to work and when you risk overheating or overcooling the home — or having no heating or cooling in situations where either is wanted.
  • Smart thermostats don’t respond to voice commands: If the batteries are too low or dead, this feature will only work once the batteries are replaced or recharged.

I Changed the Batteries in my Thermostat, but They Keep Draining Quickly.

Although the quality of the batteries used in an HVAC thermostat can affect how quickly they drain, here are three other common reasons:
  • Corroded battery contacts: Corroded contacts have a high resistance to new batteries, along with short or loose connections. Cleaning the contacts should resolve the issue, but if it doesn’t, contact your HVAC technician.
  • Incorrect battery type: Most thermostats need batteries with a 3.6 voltage or more. Though the correct size, some off-brand batteries only have a 1.5 voltage or less.
  • Old thermostat: The older the internal parts, such as sensors and wires, the more energy the thermostat needs to operate. These energy demands can drain even high-quality batteries.
  • Changing the batteries in your HVAC thermostat takes a few minutes of your day but provides reassurance of heating and cooling throughout the year.

    Contact JW Plumbing, Heating and Air

    If you need thermostat installation or service in Los Angeles, we’re here to help. Contact JW Plumbing, Heating and Air today.

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