Open the thermostat cover and locate the battery compartment

Most Honeywell Home thermostats hold two AA batteries in a compartment on the back or inside the unit. The first step is to gently pull the thermostat away from the wall—it usually snaps off the mounting plate without tools. Once it's free, look for a small door or panel on the back. This is where the batteries sit.

If your model has a battery door, it typically slides down or swings open. You may see a small arrow or line showing which direction to push. Don't force it; these doors are designed to move smoothly. If you're unsure which way it opens, check the user manual that came with your thermostat, or search for your specific model number online—Honeywell publishes PDFs for nearly every model.

Key Takeaways

  • Remove the thermostat from the wall by gently pulling it straight toward you; it snaps off the mounting plate without tools.
  • Open the battery compartment door on the back of the unit and note which direction the old batteries are facing before you remove them.
  • Replace both AA batteries at the same time, even if only one is dead, and make sure the positive and negative ends match the markings inside the compartment.
  • Snap the thermostat back onto the wall plate and check that the display lights up and shows the correct time and temperature.

Remove the old batteries and note their orientation

Once the compartment is open, you'll see two AA batteries sitting side by side. Before you pull them out, take a moment to notice which way they're facing—specifically, which end (the flat negative end or the bumpy positive end) is pointing toward the top or bottom of the compartment. Most compartments have a diagram printed inside showing the correct orientation, but if the markings are faded, a quick photo with your phone is a good backup.

Gently slide or pop out the old batteries. They may be held in place by a small spring or clip, so don't yank them. If a battery is stuck, try rocking it slightly side to side before pulling. Once both are out, set them aside—you don't need to recycle them when ready, but alkaline batteries should not go in the trash; most retailers like Best Buy or Home Depot have free battery recycling bins near the entrance.

Insert new AA alkaline batteries in the correct direction

Use two fresh AA alkaline batteries—not rechargeable, not mixed old and new. Alkaline batteries last longer in thermostats and are more reliable. Hold each battery so the positive end (the bump) faces the direction shown in the compartment diagram. Slide them in gently until they sit flat and flush with the compartment.

If the compartment has a spring clip, the batteries should sit snugly against it. You should hear or feel a small click when they're seated correctly. Do not force them; if they don't slide in smoothly, you may have the polarity reversed. Double-check the orientation and try again. Forcing batteries in the wrong direction can damage the contacts inside the thermostat.

Close the battery door and reattach the thermostat to the wall

Slide or swing the battery compartment door closed until it clicks or sits flush. Then carefully align the thermostat with the mounting plate on the wall and press it straight in. You should feel it snap into place. The thermostat should sit flat against the wall with no gaps.

Once it's mounted, the display should light up within a few seconds. If it doesn't, the batteries may not be making contact—remove the thermostat again and reseat them. If the display lights up but shows a low battery warning or a blinking symbol, the batteries may be old stock or defective. Replace them with a fresh pair and the warning should clear within a minute.

Verify the time and temperature are correct

After the display comes on, check that the time is still correct. If the thermostat lost power during the battery change, the time may have reset to 12:00 or a default time. Most Honeywell Home models let you adjust the time using the up and down buttons on the face of the unit. Consult your manual for the exact button sequence, as it varies by model.

Also confirm that the thermostat is reading the current room temperature. If it shows a number that seems way off (like 45 degrees when it's actually 70), the sensor may need time to recalibrate, or the thermostat may need to be reset. Wait five minutes and check again. If the temperature is still wrong, the sensor itself may be faulty, and you may need to contact Honeywell support or replace the unit.

Common mistakes to avoid when changing batteries

The most frequent error is inserting batteries backward. The positive end (the side with the bump) must face the direction marked in the compartment. If you reverse them, the thermostat won't power on, and you may damage the battery contacts. Always check the diagram before inserting.

Another mistake is mixing old and new batteries. Even if one battery still has charge, replace both at the same time. Mixing them causes one to drain faster and can create uneven power delivery, leading to display glitches or the thermostat losing settings. Also avoid rechargeable batteries—they have a different voltage curve and don't work reliably in thermostats.

Finally, don't forget to snap the thermostat back onto the wall plate firmly. If it's not fully seated, it may lose connection intermittently, causing the display to flicker or the thermostat to reset. Press straight in until you hear the click.

What to do if the thermostat still won't turn on

If you've installed fresh batteries in the correct orientation and the display still doesn't light up, the battery contacts inside the compartment may be corroded or bent. Open the compartment again and look at the metal contacts—they should be shiny and smooth. If they look dark, dull, or oxidized, gently rub them with a clean, dry cloth or a pencil eraser to remove the corrosion.

If the contacts look fine but the thermostat still won't power on, the unit itself may have failed. Honeywell Home thermostats typically last 10 to 15 years, but battery compartments can wear out sooner. At that point, you may need to replace the thermostat. Before you do, try removing the batteries for 30 seconds and reinserting them—this sometimes resets the internal circuit and restores power.

Frequently Asked Questions

How often do I need to change the batteries in my Honeywell thermostat?

Most AA batteries last one to two years in a thermostat, depending on the model and how often the display is lit. If your thermostat is battery-powered only (not hardwired to your heating system), the batteries will drain faster. If it's hardwired, the batteries are a backup and last much longer. Your thermostat will usually show a low battery warning on the display before the batteries die completely.

Can I use rechargeable batteries instead of alkaline?

No. Rechargeable batteries have a lower voltage (1.2 volts per cell instead of 1.5 volts) and don't deliver steady power over time. Honeywell thermostats are designed for alkaline batteries and may not function correctly with rechargeables. Stick with fresh AA alkaline batteries for reliable operation.

What if I put the batteries in backward?

If you insert both batteries backward, the thermostat straightforward won't power on. The display will stay dark. Remove the thermostat, open the compartment, flip both batteries around, and reinsert them. There's no permanent damage as long as you correct it right away. If you left them backward for more than a few minutes, the battery contacts may have been stressed, but they usually recover once you fix the polarity.

Do I need to reprogram my thermostat after changing the batteries?

If your thermostat is hardwired to your heating system, it should retain all your settings and schedules during a battery change. If it's battery-powered only, you may lose the time and any programmed schedules. You'll need to reset the time and reprogram your heating schedule using the buttons on the thermostat or the Honeywell Home app, depending on your model.

Why is my thermostat showing a low battery warning even after I put in new batteries?

The warning usually clears within one to two minutes as the thermostat recognizes the new batteries. If it persists after five minutes, the batteries may be old stock or defective—try a different brand or a fresh pack. Also check that both batteries are fully inserted and making contact with the metal terminals inside the compartment.