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Honeywell provides an extensive variety of thermostats, ranging from the straightforward 1000 series all the way up to the top-tier T10s. However, due to this broad selection, it might sometimes be difficult to precisely determine the battery replacement instructions for a specific Honeywell thermostat model. While the process of replacing the battery is generally consistent across different models, it's essential to remember that there might be slight differences occasionally.

General Instructions

Honeywell thermostats typically consist of a base plate and a cover plate, which is attached to the wall. Generally speaking, to change the battery, you turn off power to your thermostat, remove the cover plate and swap out the old batteries.

It's important to note that not all Honeywell thermostats require batteries – but if yours has an LED display, it most likely does.

Like any battery-operated device, you'll need to change the batteries periodically to ensure optimal performance.

Most Honeywell thermostats only require a battery change once a year. When the “Battery/Batt Low” indicator appears, you'll have 60 days to replace the batteries before the device ceases to function properly.

Safety Precautions & Equipment Needed

At Smart Home Perfected we always advise readers not to undertake any work they are not competent in performing and if in any doubt, it is best to seek the assistance of a professional.

Before replacing the batteries in your Honeywell thermostat, I recommended you take the necessary precautions to ensure you do it safely.

Familiarize yourself with the required battery type (usually AA or AAA alkaline batteries) and the correct number needed for your specific model.

It's crucial to match the battery polarity with the markings on the compartment to avoid causing damage to your thermostat.

I've compiled a helpful list of popular Honeywell thermostat manuals to guide you in identifying whether your device requires batteries and the appropriate kind to use.

Replacing batteries in a thermostat that features a non-sliding compartment is easy. Even though thermostat wiring is generally 24 volts (in the US), I recommend starting by turning off the power supply to the thermostat to prevent any potential electrical hazards.

To access the battery compartment, gently pull the cover plate away from the bottom, wiggling it if necessary, until it detaches from the base plate.

In some instances, it may be necessary to remove a small screw at the base before separation. 

Always exercise caution while removing the cover plate to avoid damaging any pins or clips.

Finding the Model Number

Generally speaking, the model number of your thermostat is either referenced on the front of the device, is accessible through the digital interface, or is printed on a label at the back. In the model-specific instruction below, I’ve included images and diagrams to help you identify the right model.

T10 Pro & T9

The T10 Pro and T9 thermostats from Honeywell don't require battery replacements, as they use the C (standard) wire to draw power from the HVAC transformer, operating with a 24-volt supply.

However, their wireless indoor sensors rely on AAA alkaline batteries.

Keep an eye on the thermostat screen for any battery warnings, which usually appear about 60 days before the batteries are completely drained.

If the sensor status light starts flashing red, this means the battery charge is critically low, with only 2-3 weeks of use remaining. During regular operation, the status light remains switched off.

To replace the batteries in your indoor sensor, follow these simple steps:

  1. Remove the sensor cover.
  2. Insert two new AAA alkaline batteries.
  3. Upon installation, the status light will flash green if the batteries are in good condition, and red if they need immediate replacement.
  4. After replacing the cover, the sensor will automatically reconnect with the thermostat within a few seconds.

Remember to use new, high-quality AAA alkaline batteries to ensure optimal performance and prolonged sensor life for your T10 Pro or T9 thermostat.

T6 Z-Wave

The T6 Z-Wave thermostat offers flexibility in its power source, allowing it to function with either battery power (using 3 x AA batteries) or 24 VAC power through a “C” or common wire.

The choice is optional: batteries can provide backup power when the thermostat is wired to operate on 24 VAC, though not necessary altogether.

All non-battery-operated Z-Wave devices within the network will serve as repeaters, regardless of the manufacturer, ensuring a reliable connection throughout the network.

To maintain optimal functionality, it is vital to promptly replace the thermostat batteries when the low-battery alert appears—typically around two months before full depletion.

You can change the battery of a Honeywell T6 Z-Wave thermostat by:

  1. Locate the battery compartment.
  2. Open the compartment using a screwdriver or latch release tool.
  3. Remove the old batteries and dispose of them properly.
  4. Insert fresh batteries of the same type, observing the correct polarity.
  5. Close the battery compartment securely.
  6. Test the thermostat to ensure it powers on and displays the correct settings.
  7. Reconfigure the Z-Wave network if necessary, following the manufacturer's instructions.

Below is a diagram of how to change the batteries on this model

honeywell thermostat battery
image 61

T4 Pro

The T4 Pro offers smart technology that helps you save on energy costs. Its clear and accurate display ensures optimal temperature control, and its compatibility with most heating and cooling systems makes it a versatile choice for any home. 

You can wire your T4 Pro to run on AC power. Alternatively, you can power it using 2 AA batteries. To replace these batteries, follow these steps:

  1. Locate and remove the battery compartment cover.
  2. Take out the old batteries.
  3. Insert the new batteries, ensuring correct polarity.
  4. Reinsert the battery compartment cover.
  5. Verify the proper functioning of the thermostat.

Below is a diagram of how to change the batteries on this model

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8000 Series

A complete touchscreen controller and Wi-Fi compatibility are two new feature upgrades in the 8000 series. In a nutshell, the 8000 series underwent a complete revamp, which sets it apart from its predecessors. Using the new features, you can adjust the humidity, ventilation, program schedule, and other things, just by using your smartphone.

This series is also compatible with Honeywell’s “My Total Connect Comfort” web portal. It also has an app that allows its users to control their thermostats.

This series covers models TH8110U, TH8320U & TH8321U.

Make sure your 8000 series thermostat is always operational with these steps:

  1. Turn off your thermostat.
  2. Hold the cover plate and gently pull it to detach from the base plate.
  3. Replace all three AAA batteries, aligning with the battery compartment markings.
  4. Reattach the cover plate to the base plate.
  5. Power on your thermostat and enjoy renewed device functionality.

Below is a diagram of how to change the batteries on this model

image 66

6000 Series

This series comes with a sliding battery slot, as well as a few other upgrades to the control system compared to previous models.

Along with hardware upgrades, this series also introduced some software upgrades such as the Program Schedule feature. Using this, you can program different settings for different weekdays and weekends. This feature has four pre-set settings which can greatly help when it comes to saving on energy costs.

This series covers models TH6110D, TH6220D & TH6320U.

To change the battery of a Honeywell 6000 series thermostat, do the following:

  1. Switch off your thermostat.
  2. Press and pull the cover plate to remove the battery holder at the top-right corner.
  3. Take out the battery compartment.
  4. Replace both AA batteries.
  5. Attach the cover plate back onto the base plate, sliding it firmly.
  6. You can power your thermostat back on.

Below is a diagram of how to change the batteries on this model

image 62

5000 Series

This series introduced the sliding battery compartment slot. As a result, to change the battery, you no longer need to separate the cover plate from the base plate.

This series also includes the Auto Changeover feature. On many occasions, you might need to use both heating and air conditioning on the same day. The Auto Changeover feature makes this possible. It automatically selects between heating or cooling after assessing the indoor temperature.

This series covers models Focus Pro, TH5110D, TH5320U & TH5220D.

Follow these steps to change the battery of your Honeywell 5000 series thermostat:

  1. Turn off your thermostat.
  2. Locate the battery holder at the top-right corner of the cover plate, then press and gently pull to remove it.
  3. Remove the battery compartment.
  4. Replace the two AA batteries with fresh ones, ensuring the polarity matches the markings on the compartment.
  5. Place the cover plate back onto the base plate.
  6. Turn your thermostat back on, now running on fresh batteries.

Below is a diagram of how to change the batteries on this model

image 65
image 64

4000 Series

Just like its predecessors, this series also features a built-in compressor protection system. You can set your desired temperature, control the fan, and adjust the emergency heating system using the control system.

This series comes with an upgraded LED display that will notify you when the battery is running low and will display the current indoor temperature, the current day & time, and the current system status, among other useful metrics.

The 4000 series covers models TH4210D & TH4110D.

Below is a walkthrough of the simple process of replacing the batteries in your 4000 Series thermostat, ensuring your home stays comfortable and energy-efficient:

  1. Switch off your thermostat and isolate the circuit as a precaution.
  2. Place your fingers at the bottom of the thermostat and pull to remove the cover plate.
  3. Replace both AA batteries with new ones.
  4. Make sure the battery polarity matches the markings on the battery compartment.
  5. Set the cover plate back in its place by sliding it onto the base plate until it's firmly fixed.

Below is a diagram of how to change the batteries on this model

image 67
image 68

3000 Series

A built-in compressor protection feature sets this series apart from others. This feature protects the compressors in your air conditioner and heat pump. Moreover, it hosts a control system and a display screen.

The 3000 series uses batteries to withstand fluctuations in the AC power supply. Nonetheless, it might need a battery replacement once a year. You will receive an alert 2 months before complete battery depletion.

Upgrading your Honeywell Thermostat 3000 series’ battery ensures smooth operation all year round. This series includes model numbers TH3110D1008 and TH3210D1004.

Here is a concise step-by-step guide to make the process hassle-free: 

  1. Turn off the thermostat, and isolate the circuit for safety.
  2. Gently pull the bottom of the thermostat to separate the cover plate from the base plate.
  3. Remove the old batteries and insert new ones, ensuring correct polarity alignment.
  4. Slide the cover plate back onto the base plate.
  5. Turn on the thermostat and circuit, and enjoy uninterrupted climate control in your home.

Below is a diagram of how to change the batteries on this model

image 69
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RTH2300 / RTH221 Series

The Honeywell RTH2300/RTH221 Series is a user-friendly programmable thermostat designed to enhance your home's comfort and energy efficiency. 

With a sleek design and intuitive interface, this series lets you easily program your desired temperature settings and schedule throughout the day. It offers precise temperature control, ensuring a comfortable environment while helping to reduce energy consumption.

This series covers models RTH2300B, RTH2300, RTH221

You can change the battery of these thermostats by following these steps:

  1. Open the battery compartment on the back.
  2. Remove the old batteries.
  3. Insert the new batteries, ensuring correct polarity.
  4. Close the battery compartment.
  5. Verify the proper functioning of the thermostat.

Below is a diagram of how to change the batteries on this model

image 74
image 73

1000 & 2000 Series

Honeywell 1000 and 2000 series thermostats are popular among those who are on a budget. These two series are widely used in multi-family households and apartment complexes.

Each model from these two series comes with an LED display for easier control. Whether you intend on using them with your air conditioner or your gas furnace, they’ve got you covered.

The 1000 series includes models TH1100DV, TH1110DV, TH1210DV, and the 2000 series includes models TH2110DV, and TH2210DV. Here’s how to change the battery of each of them:

  1. Carefully remove the cover plate from the base plate.
  2. Swap out the old AAA batteries with fresh ones.
  3. Align the battery polarity according to the compartment markings.
  4. Replace the cover plate, securing it onto the base plate.
  5. Switch the thermostat and circuit back on to complete the process.

Below is a diagram of how to change the batteries on this model

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Common Honeywell Thermostat Battery Questions

What are the best batteries to use?

Some Honeywell thermostats use alkaline AA batteries, while others use alkaline AAA ones. 

If you are not sure which ones your thermostat requires, check the old batteries already installed on the device. That might give you an idea, or you can also check the user manual for your thermostat model.

How to clear low battery from display after Honeywell Thermostat battery replacement?

Soon after you replace the old batteries, the “Low Battery” sign will automatically disappear. If not, you may need to power down and power up the device to reset it. This may need to be done at the circuit breaker.

Honeywell thermostats store your settings in their memory. So even when you dismantle them to insert new batteries, they will remember your settings once they start running again.

The thermostat still won't work after replacing the batteries, what should I do?

It can happen for a couple of reasons. Check if the battery polarity matches the markings on the battery compartment of the thermostat. 

If it matches and your thermostat still doesn’t work, try using the batteries in another device to check if they are draining or not.

If the thermostat still doesn’t work, you should contact the Honeywell support team.

What happens when the batteries go dead?

After the “Low Battery” sign starts to flash, you will typically have 60 days to replace the batteries. Your thermostat might also display a blank screen to save energy.

If you still fail to change the batteries, after 60 days they will be depleted of energy and your thermostat will stop functioning.

What is the Honeywell thermostat battery size?

Not all Honeywell thermostats require batteries. But some do, usually the ones with an LED display.

All the thermostats that require batteries need 2 or more alkaline AA or AAA types.

Why is my Honeywell thermostat showing as battery low?

This is how your Honeywell thermostat notifies you about its low battery life. The “Battery Low” message is displayed on the LED screen 60 days before complete depletion.


And that's it – you're now equipped to replace the Honeywell thermostat battery in a variety of models, from the classic 1000 and 2000 series to the advanced T10 Pro.


Show CommentsClose Comments


  • Trudy Yates
    Posted October 14, 2022 at 1:42 pm

    Hi I have a vertical Honeywell thermostat that started blinking low battery last month and I’ve tried to get maintenance to come change the batteries but my apt complex is under new management since the end of this past May and they’re not as dependable as the other landlord I had here for the past 13 yrs.
    Anyway the cover plate does not pull off and I noticed it has a tiny screw on the underside of it and not easy to get to. The thermostat was changed 5 yrs ago and I wasn’t given the owners manual so I have no model number. Any positive feedback would be greatly appreciated.
    Thank you
    P.S. I took picture of it and have it on my phone if that would help?

    • Trudy Yates
      Posted October 14, 2022 at 1:46 pm

      Also not sure if it takes AA or AAA batteries but I bought both.
      I’ve never had to change the batteries in the past but it’s been a month and I read online where you have about 60 days before the batteries stop working completely.

      • Daniel Walsh
        Posted May 16, 2023 at 10:54 am

        Hi Trudy, the vertical thermostat is likely the 1000 series which has 2 AAA batteries. You can find the instructions for that series above.

  • Janis
    Posted June 15, 2022 at 5:03 pm

    Does the 2 AA batteries have to be alkaline batteries?

    • Daniel Walsh
      Posted May 16, 2023 at 10:55 am

      Generally speaking Yes. New, Alkaline batteries are recommended as opposed to rechargeable or lithium.

  • Jennifer A. Garner
    Posted February 7, 2022 at 1:50 am

    Took off the front cover of my thermostat. Do not see batteries but something that looks like a computer chip. Please help.

    • Drew
      Posted June 19, 2022 at 1:57 am

      Check the float switch and/or furnace door. I have the same unit and had to make sure the door was completely shut. I also jiggled the float switch and it came back on.

  • Nikos Liaros
    Posted January 24, 2022 at 8:35 am

    Hello. I have an older model Honeywell thermostat and I need to change the batteries but I dont have the instructions. Can you please give me your mail so i can send you a photo ? You might be able to identify the model series from the photo and give me instructions.

  • Leslie
    Posted December 19, 2021 at 6:11 pm

    I have an RTH6580WF1001. I am able to get it off the wall but am unable to get inside to replace the batteries. Please lmk.

    Posted November 23, 2021 at 3:55 am

    Mine is Lyric TH6220WF2006. Once I remove the unit there is no battery.

  • Christine
    Posted November 9, 2021 at 9:42 pm

    What if I can’t find the model number? I’m house sitting light is flashing replace battery – I don’t want to pull from wall. I have a pic of thermostat if that helps identify it

  • Darius Daver
    Posted October 29, 2021 at 11:09 pm

    I have a Honeywell CM907. Can i just switch unit off and change batteries or do i need to turn power off please?

    • Daniel Walsh
      Posted May 16, 2023 at 10:59 am

      I always recommend turning off power at the breaker just in case

  • Christopher Roe
    Posted September 27, 2021 at 7:49 pm

    I have a Honeywell TH8321R1001. I did not find any information on changing the batteries on this site. This type takes 4 aa batteries plus a round cr2032lithiuem. How often should these be changed?

  • Rich Guion
    Posted August 7, 2021 at 8:23 pm

    how do I REPLACE the lithium battery In my TH9320WF5003 HONEYWELL thermostat? I have tried a million times in Google and Honeywell support to find out how to REPLACE the lithium battery in my TH9320WF5003 HONEYWELL thermostat? I now know how to change batteries in every Henwell thermoset that ever existed accept my TH9320WF5003!

    Have a God Blessed day,

    • Daniel Walsh
      Posted May 16, 2023 at 11:02 am

      Hi Rich – It’s possible its a non-serviceable part – best to contact Honeywell support to confirm

  • Richard Rhea
    Posted February 28, 2021 at 12:56 pm

    I need to change the AA batteries on my Honeywell Model #THX9421R5021. You don’t list this model. Would very much a step by step procedure in order to change them.

    Posted February 23, 2021 at 12:05 pm

    The model number of our Honeywell Thermostat (on the back of the unit) is TH8320WF. Just noticed that the User Guide and the Quick Start Guide refer to models RTH8580WF and RTH8500WF Wi-Fi Series. The screen has gone totally blank. Are there batteries to be replaced? If so, where…..and how?

    • Daniel Walsh
      Posted February 23, 2021 at 3:23 pm

      Hi Larry

      The TH8320WF VisionPro does not have a serviceable battery (it has an internal lithium battery). If you have a blank screen it is recommended to …

      • Check circuit breaker and reset if necessary.
      • Make sure power switch at heating and cooling system is on.
      • Make sure furnace door is closed securely.
      • Make sure C wire is connected.

      You can find the correct manuals for the TH8320WF on this page –

      If none of the above work you may need to replace the unit or seek the services of a HVAC professional

      Hope this helps


    • Herb Cornelius
      Posted January 1, 2022 at 6:22 pm

      I know this is too late to help you, but maybe it will help someone else. On my unit, when the condensation pan is full the float switch turn off power to everything, including the thermostat. I thought I had a battery issue too, but not.

  • Rosa Tebovici
    Posted February 15, 2021 at 4:31 pm

    I need to change the battery’s on Honeywell TL8100. How is the cover removed. Do I need tools?

    • Daniel Walsh
      Posted February 15, 2021 at 5:03 pm

      Hi Rosa,

      We have the manual for the TL8100 listed on our manuals page here –

      It references a battery replacement however does not provide step by step instructions. If you are competent at DIY and wiring, then the process is to isolate the circuit to avoid exposure to live wiring. Then unscrew the front plate at the bottom and remove the cover. Be careful not to damage the pins or clips when uncovering.

      You should then have access to the battery compartment to replace the batteries.

      If the above is a bit too much, then I recommend seeking the services of a local HVAC professional to carry out the process. We have a form above which you can fill out to get a quote.

      Hope this helps


  • David
    Posted January 14, 2021 at 12:29 am

    My thermostat went blank . The Model# is TH632OWF2003. I can’t locate a battery to replace any suggestions?

    • Daniel Walsh
      Posted January 14, 2021 at 2:52 pm

      Hi David,

      You can access the manual for the TH6320WF on our manuals page –

      To troubleshoot a blank screen for that model, it is recommend to …

      • Check circuit breaker and reset if necessary.
      • Make sure power switch at heating and cooling system is on.
      • Make sure furnace door is closed securely.

      I don’t believe there is a replaceable battery in that specific model as it runs off 24v power.

      Hope this helps


  • Louis Hanson
    Posted December 23, 2020 at 12:45 am

    My thermostat quit working and shows “lo bat” in the upper right hand corner. It looks like the picture of Model RTH 221B1039 but I’m not sure that’s right. I can not see how to remove the cover to get at batteries.

  • Vickie
    Posted November 21, 2020 at 2:41 pm

    I just changed my batteries and when I turn it to “on” instead of “auto” it goes on but I don’t have a display anymore. I think mine is the 1000-2000 series. How do I get the display back? I use the display for temperature settings. 🙁

  • Judy R.
    Posted November 5, 2020 at 9:29 am

    My Honeywell thermostat t8112d1005 read Bat Lo and I replaced the batteries according to the instructions on the unit. It was still showing battery low so I put another set of fresh batteries in and no change. Now the furnace won’t turn on at all and the battery low readout just sits there. I can’t adjust the settings. Is it time for a new thermostat or is there something I can do to reset it?

    • Daniel Walsh
      Posted November 5, 2020 at 10:03 am

      Hi Judy,

      For that model, it is recommended when changing the batteries to leave it one hour between removing the old batteries and replacing them with new ones. If that doesn’t work, you can try to put the new batteries in backward, and turn on the device for 10 seconds. Then put them back in correctly. That can sometimes reset the Bat Lo indicator.

      You can access the user manual for the T8112D here –

      The T8112D is a relatively old unit. If it can no longer draw power from new batteries and the above does not work, then yes it may be time for a replacement. If your HVAC system is due a service, it might be worth reaching out to a professional who can replace the thermostat and inspect the system.

      Hope this helps


  • Federico
    Posted October 29, 2020 at 8:16 am

    Can you tell me which current Honeywell thermostats would be a replacement to the old model T874D1165?

    • Daniel Walsh
      Posted October 29, 2020 at 8:47 am

      Hi Federico

      It looks like the T874 D 1165 is a two-stage heating & cooling thermostat that supports heat pump systems.

      Without understanding the exact heating system and wiring configuration it’s hard to provide a definitive recommendation. The “T6 Pro Smart Thermostat” could work as it supports multi-stage heating and cooling and can be integrated with a heat pump system. However, professional installation is recommended.

      There is a compatibility checker on the T6 Pro product page which would be worth checking to see if it a good replacement –

      You would need to take a look at the existing wiring to see if there is a C-Wire being used. (Might not be as the T874 D 1165 is an analog thermostat) – Most modern thermostats require a C-Wire to provide continuous power to the display. Without a C-Wire, you would either need to install one (Big job), re-use the fan wire, or select a digital thermostat that doesn’t require a C-wire (i.e. one that has batteries)

      Hope this helps


  • Cindy
    Posted October 21, 2020 at 9:11 pm

    I have an old thermostat number T8624D2004N
    Has blank screen. I have it off the plate piece cant find battery compartment. The N in the number kind of looks like a sideways 2

    • Daniel Walsh
      Posted October 22, 2020 at 3:08 am

      Hi Cindy,

      We have the user guide and installation manual for that model on our manuals page here –

      Essentially that model does not contain batteries and is powered directly from the RH / RC and C wires from the furnace.

      If you have a blank screen, its typically a power issue. It’s best to check if the circuit breaker is tripped and if so reset it. Or the HVAC system fuse may be blown and if so replace it. If your HVAC system has a power switch make sure it is in the On position. The wiring may have become frayed between the furnace and thermostat so you could also check that.

      If none of the above works, its best to follow the troubleshooting guide in the manuals.

      Hope this helps


  • Sarah McIntyre
    Posted September 21, 2020 at 12:19 pm

    I can’t figure out how to open my thermostat to replace batteries. I think my model # is T8400B 1018 (2), or maybe 0330 2C. I don’t even know if my thermostat runs on batteries, but anyway, it isn’t working at all and it’s getting kind of cold in here. The furnace itself is working fine; I know because I have hot water. Please advise.

    • Daniel Walsh
      Posted September 22, 2020 at 2:29 am

      Hi Sarah,

      The T8400B 1018 isn’t powered by batteries and instead is powered directly through the heating system controls. It also doesn’t have backup batteries, to hold the programming in case of a power outage. I can’t find any specific manuals on 0330 2C so not sure.

      It may be time to call in a heating specialist as there may be a bigger issue to be resolved with the system to get it back up and running.

      Sorry I can’t be more help!

  • Nancy Sullivan
    Posted September 18, 2020 at 3:40 pm

    I have a thermostat that was installed in 2010. It’s 4 1/2″ by 6 ” and is totally LED – no buttons. I have the HVAC system serviced ever year. I don’t know what model it is, and to my knowledge the batteries have never been replaced (if there are batteries). I called the company that installed it and they were not helpful, however, they are willing to come out and check it for $90. If it’s batteries I would like to replace them myself — but I’ve pulled on the cover and it does not easily come off. Any suggestions?

    • Daniel Walsh
      Posted September 22, 2020 at 2:40 am

      Hi Nancy,

      Without an exact model number, it’s hard to diagnose.

      Is there a particular reason you would like to change the batteries – is the thermostat malfunctioning, LED display off or display showing a low battery sign?

      Some thermostats have backup batteries (which hold your specific heating programming in memory during a power outage), which are typically alkaline batteries.

      Other thermostats are powered directly by alkaline batteries, as opposed to the the heating system.

      Typically alkaline batteries wouldn’t last 10 years with regular use powering an LED display, so if the display is still working fine and there are no “low battery” messages then its possible your model does not have batteries and is powered directly by the heating system.

      Hope this helps!


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