Most Honeywell thermostats use two AA or AAA batteries in a compartment behind the faceplate
The exact battery type depends on your model, but the process is the same: remove the faceplate, locate the battery compartment (usually a plastic tray or slot), slide out the old batteries, and insert new ones with the correct polarity. The whole job takes about two minutes and requires no tools. Your thermostat will show a low-battery indicator on the display before the batteries die completely, giving you time to replace them before the system stops responding.
If you are not sure which model you own, look at the front of the thermostat or check the documentation that came with your home. Honeywell makes dozens of models—programmable, smart, and basic digital versions—but nearly all use standard AA or AAA alkaline batteries as a backup power source. The batteries keep your thermostat running if the power goes out and preserve your settings if you lose electricity.
Key Takeaways
- Most Honeywell thermostats use two AA or AAA alkaline batteries located behind the removable faceplate.
- The thermostat will display a low-battery warning on the screen before the batteries fail completely.
- Replace both batteries at the same time, even if only one appears dead, to avoid power loss mid-cycle.
- Insert new batteries with the positive (+) end facing the correct direction, as shown in the compartment.
- If the thermostat does not respond after you replace the batteries, check that they are seated firmly and the polarity is correct.
Locate and remove the thermostat faceplate
Most Honeywell thermostats have a faceplate that snaps or slides off the wall plate. Look for a small slot or notch along the edge of the faceplate—usually on the bottom or side—and gently pry it away from the base with your fingernail or a plastic card. Do not use a metal tool, which can scratch the plastic or damage the electronics inside.
If the faceplate does not budge, check whether it is held by a screw. Some older Honeywell models have a single screw at the bottom. Loosen it with a screwdriver and the faceplate will slide down or lift away. Once the faceplate is off, you will see the battery compartment clearly marked on the wall plate or the back of the faceplate itself.
Find the battery compartment and note the polarity
The battery compartment is a small plastic tray or slot with two metal contacts. Look inside and you will see a diagram showing which end of each battery goes where—usually a + symbol for positive and a − symbol for negative. This polarity marking is critical: batteries installed backward will not power the thermostat and may damage the contacts over time.
If the diagram is faded or missing, remember the standard rule: the positive end (the flat or slightly raised end marked +) faces toward the spring or contact inside the compartment. Take a photo of the compartment with your phone before you remove the old batteries so you have a reference if you forget the order.
Remove the old batteries and insert new ones
Slide or pop out the old batteries from the compartment. If they are stuck, gently wiggle them side to side while pulling. Once both are out, insert two fresh AA or AAA alkaline batteries (depending on your model) with the positive end facing the direction shown in the compartment. Push them in firmly until they sit flat and make contact with the metal springs.
Do not mix battery types—use two of the same size and brand if possible. Alkaline batteries (the standard kind sold in most stores) work best for thermostats. Rechargeable batteries are not recommended because they lose charge faster and may not provide stable power to the thermostat's electronics.
Reattach the faceplate and test the display
Slide or snap the faceplate back onto the wall plate until it clicks or sits flush. The thermostat should power on when ready and display the current temperature and time. If the screen remains blank or shows garbled text, remove the faceplate again and check that both batteries are seated firmly and facing the correct direction.
Once the display is working, your thermostat will resume normal operation. If you had a power outage before replacing the batteries, your programmed schedule and settings should still be intact because the batteries preserved them while the main power was off. The low-battery warning should disappear from the screen.
When to replace batteries and what to watch for
Most alkaline AA or AAA batteries last one to two years in a thermostat, depending on how often the thermostat switches the heating or cooling system on and off. You will see a low-battery indicator—usually a small battery icon or the words "Low Batt"—appear on the display weeks before the batteries die. When you see this warning, replace both batteries within the next week or two.
If your thermostat stops responding to button presses or the display goes dark, dead batteries are the most common cause. Replace them first before calling a technician. If the thermostat still does not work after you install fresh batteries and check the polarity, the issue may be a loose wire connection or a faulty circuit board, which requires professional service.
Frequently Asked Questions
What happens if I install the batteries backward?
The thermostat will not power on and the display will remain blank. No damage occurs if you catch the mistake within a few minutes. straightforward remove the faceplate, flip the batteries to the correct polarity, and reinsert them. If the thermostat still does not work after you correct the polarity, remove the batteries for 30 seconds, then reinsert them to reset the circuit.
Can I use rechargeable batteries in my Honeywell thermostat?
Rechargeable batteries are not recommended. They have a lower voltage than alkaline batteries and discharge faster, which can cause the thermostat to lose power unexpectedly or fail to hold your settings during a power outage. Stick with standard alkaline AA or AAA batteries from a grocery store or hardware store.
How do I know which battery size my thermostat uses?
Check the battery compartment itself—the tray or slot will be sized for either AA or AAA batteries, and the difference is obvious when you look at it. You can also check your thermostat's manual or look up your model number on Honeywell's website. The model number is usually printed on a sticker on the back of the wall plate.
Will my thermostat lose its settings if the batteries die?
No. Your programmed schedule and temperature settings are stored in the thermostat's memory, which is powered by the batteries. As long as you replace the batteries within a few hours of them dying, your settings will remain intact. If the batteries are dead for more than a day, you may need to reprogram the thermostat.
What should I do with the old batteries?
Take them to a battery recycling program or a retailer that accepts used batteries—most hardware stores and electronics retailers have a drop-off bin near the entrance. Do not throw alkaline batteries in the trash if your local regulations prohibit it. Check your city or county's hazardous waste disposal guidelines for details.