Replace the battery by opening the thermostat cover, noting which terminals the old battery connects to, and sliding in a fresh one of the same type

Most Honeywell thermostats use one or two AA or AAA batteries that sit in a compartment behind the faceplate. The whole job takes under five minutes. You do not need tools, and the thermostat will keep your heating and cooling settings after you swap the battery — it stores them in memory even when power is off.

The first step is to turn off power at your breaker if your thermostat is hardwired to your HVAC system. If it runs on batteries alone, you can skip this. Then gently pry the faceplate away from the wall using your fingernail or a plastic card. Most Honeywell covers snap on and off without fasteners.

Inside, you will see the battery compartment, usually a plastic tray with two metal contact points. Slide the old battery out, note which end (positive or negative) faces which direction, and slide the new battery in the same way. Close the cover and power the thermostat back on at the breaker if you turned it off.

Key Takeaways

  • Honeywell thermostats typically hold one or two AA or AAA batteries in a compartment behind the faceplate, which snaps off without tools.
  • Your thermostat will retain all saved temperature settings and schedules even when the battery is removed, because they are stored in memory.
  • Always note which direction the old battery faces before removing it, so you can insert the new one the same way.
  • If your thermostat is hardwired to your HVAC system, turn off power at the breaker before opening the cover to avoid electrical shock.
  • A fresh battery usually lasts one to two years, depending on how often your thermostat switches your heating or cooling on and off.

Identify your thermostat model and battery type

Honeywell makes dozens of thermostat models, and not all use the same battery. The most common types are AA alkaline, AAA alkaline, and 3V lithium coin cells. Check the label on the back of your thermostat or inside the battery compartment — it will say what size and type you need.

If you cannot find a label, look at the battery compartment itself. If it holds two round metal cylinders side by side, you have AA batteries. If the compartment is smaller and narrower, you have AAA. If you see a flat circular battery about the size of a dime, you have a coin cell, which is less common but still straightforward to find at any drugstore.

Write down the model number before you go to the store. It usually starts with "T" or "RTH" and appears on a sticker on the back of the thermostat or inside the battery door. This way, if you have questions at the store, you can confirm the right battery type.

Open the thermostat cover without damaging it

The faceplate of a Honeywell thermostat is held on by plastic clips, not screws. To remove it, start at the bottom edge and gently work your fingernail or a plastic card (like an old gift card) under the lip. Do not use a metal tool — it can scratch the plastic or damage the clips.

Once you have lifted the bottom edge slightly, move to the sides and work your way up. You will feel the clips release as you go. The cover should come free with light, steady pressure. If it feels stuck, stop and try a different spot — forcing it can break the clips.

Set the cover aside on a clean surface where you will not lose it. Some people place it upside down on a table so the clips face up and you can see how they fit when you put the cover back on.

Remove the old battery and note its position

Before you touch the old battery, look at how it sits in the compartment. The positive end (marked with a + sign) should face a certain direction — usually toward the top or toward one of the metal contacts. Take a photo with your phone if you are unsure, or straightforward remember which end is which.

Slide the old battery out gently. If it is stuck, do not force it. A little wiggling side to side usually frees it. Once it is out, you can throw it away or recycle it if your area has a battery recycling program.

If your thermostat holds two batteries, remove them one at a time and note the position of each. Some compartments have the batteries arranged in a line, and others have them stacked. The metal contacts in the compartment will show you which end of each battery should face which direction.

Insert the new battery in the correct direction

Take your new battery and slide it into the compartment the same way the old one faced. The positive end should align with the metal contact marked + (if there is one), and the negative end should face the other contact. If you put it in backward, the thermostat will not turn on, but you will not damage anything — just flip it around.

Slide the battery in slowly until you feel it seat against the metal contacts. You should hear or feel a small click. Do not force it — if it does not slide smoothly, check that you are going in the right direction.

If your thermostat takes two batteries, repeat this step for the second one. Make sure both are seated firmly before you close the cover.

Close the cover and restore power

Align the top edge of the faceplate with the top of the thermostat body and press down firmly. You should feel the clips snap back into place. Work your way down the sides and bottom, pressing until the cover sits flush against the wall.

If your thermostat is hardwired to your HVAC system, turn the power back on at the breaker. The display should light up within a few seconds. If it does not, turn the power off again, open the cover, and check that the battery is seated correctly and facing the right direction.

Once the display is on, check that your temperature settings and any schedules you programmed are still there. They should be, because Honeywell thermostats store this information in memory even when the battery is out.

Troubleshoot if the thermostat does not turn on

If the display stays dark after you close the cover and restore power, the most common cause is a battery inserted backward. Open the cover again and flip the battery 180 degrees, then close the cover and check the display.

If the display still does not light, the battery itself may be dead. This is rare with new batteries, but it happens. Try a different battery of the same type. If that works, the first battery was faulty and you can return it to the store.

If neither battery works, your thermostat may have a deeper problem — a failed circuit board or a broken connection inside the battery compartment. At that point, you will likely need to replace the thermostat itself. A new Honeywell thermostat costs between $100 and $300 depending on the model and features.

Know when to replace the battery again

A fresh AA or AAA alkaline battery in a Honeywell thermostat usually lasts one to two years. If your thermostat is in a very cold climate or switches your heating on and off many times a day, the battery may drain faster. Lithium coin cells last longer — often three to five years — but they cost more upfront.

Your thermostat will show a low-battery warning on the display when the battery is running out. This warning gives you time to buy a replacement before the battery dies completely. Do not wait until the display goes dark — replace it as soon as you see the warning.

Mark your calendar for a battery check once a year, even if you do not see a warning. This way you can replace it on your schedule rather than in an emergency, and you will never be without heating or cooling because the thermostat lost power.

Frequently Asked Questions

Will my thermostat lose my temperature settings if I remove the battery?

No. Honeywell thermostats store your settings in memory, so they stay in place even when the battery is completely out. You will not lose any schedules, temperature preferences, or other settings you have programmed.

Can I use a rechargeable battery in my Honeywell thermostat?

Rechargeable batteries work, but they are not ideal. They hold less charge than alkaline batteries and may not last as long between charges. Stick with alkaline AA or AAA batteries unless your thermostat manual specifically says rechargeable batteries are okay.

What happens if I put the battery in backward?

The thermostat will not turn on, but nothing will break. straightforward open the cover, flip the battery around, and close the cover again. The display should light up right away.

Do I need to turn off my HVAC system before changing the battery?

You should turn off power at the breaker if your thermostat is hardwired to your heating and cooling system. This prevents electrical shock and protects the thermostat's circuits. If your thermostat runs on batteries alone, you do not need to turn anything off.

How do I know which battery type my thermostat needs?

Check the label inside the battery compartment or on the back of the thermostat. It will say AA, AAA, or the specific type. If you cannot find a label, look at the compartment size — AA batteries are larger and wider than AAA, and coin cells are flat and round.