Where the battery is and what you need

Most Honeywell thermostats use one or two AA or AAA batteries, depending on the model. The battery compartment is usually on the back of the thermostat or behind the faceplate. You will need a fresh battery (or two) of the correct size — check your thermostat's manual or the inside of the compartment itself, which often prints the size required.

Before you start, turn off power to your thermostat at the breaker if it is hardwired. Battery-only models do not need this step. Have your new batteries ready and keep the thermostat away from moisture while you work.

Key Takeaways

  • Most Honeywell thermostats hold one or two AA or AAA batteries in a compartment on the back or behind the faceplate.
  • Turn off power at the breaker before opening a hardwired thermostat to avoid electrical shock.
  • Note the direction the old battery faces (+ or − side) before removing it, so you install the new one the same way.
  • If your thermostat displays a low-battery warning, change the battery within a week to avoid losing your settings.
  • After installation, your thermostat may reset to factory defaults — you may need to reprogram the schedule.

How to access the battery compartment

If your thermostat has a removable faceplate, gently pull it straight toward you. Some models have a small notch or tab on the bottom edge — use your fingernail or a plastic tool to pry it loose. Do not use a metal screwdriver, which can damage the plastic or cause a short.

If there is no faceplate, the battery compartment may be on the back of the unit itself. Look for a small rectangular door or cover, usually marked with a battery symbol. Slide it to the side or press a small release button to open it. If you cannot find the compartment, check the manual for your specific model number — Honeywell makes dozens of thermostat types, and the location varies.

Removing the old battery and installing the new one

Look at how the old battery sits in the compartment. Note which end faces up — the + (positive) side or the − (negative) side. This matters. Gently push the battery toward the spring contact at one end, which will release the other end. Slide it out and set it aside.

Insert the new battery the same way the old one faced. Push it gently until the spring contact holds it in place. You should hear or feel a small click. Do not force it — if it does not slide in smoothly, you may have the polarity reversed. Remove it, flip it, and try again.

If your thermostat uses two batteries, repeat this process for the second compartment. Make sure both are installed in the correct direction.

Closing the compartment and checking for power

Slide the battery cover back into place or snap the faceplate back on. Make sure it sits flush and does not rattle. If you turned off the breaker, turn it back on now.

The display should light up within a few seconds. If it does not, the battery may be installed backward or the compartment may not be fully closed. Open it again, check the polarity, and make sure the battery is seated all the way in.

What happens to your settings after a battery change

Some Honeywell models hold your schedule and settings in memory even during a battery change. Others reset to factory defaults — usually 68 degrees Fahrenheit during the day and 62 degrees at night. Check your display to see if your schedule is still there.

If it has reset, you will need to reprogram your heating and cooling schedule. Refer to your manual for the steps, as the process differs between models. Write down your preferred temperatures and times before you start, so you do not have to guess.

Signs your battery needs changing soon

Most Honeywell thermostats display a low-battery icon or message on the screen — usually a battery symbol with an X through it, or the words "Low Batt" or "Replace Battery." When you see this, change the battery within a week. A dying battery can cause the thermostat to lose power briefly, which may reset your schedule.

If your thermostat stops responding to button presses or the display goes blank, the battery is dead. Install a fresh one and the unit should come back to life. If it does not, the thermostat itself may have a hardware problem unrelated to the battery.

Frequently Asked Questions

Can I use rechargeable batteries in my Honeywell thermostat?

Rechargeable batteries work but are not ideal. They hold less voltage than alkaline batteries and may drain faster, triggering low-battery warnings more often. Stick with fresh alkaline AA or AAA batteries for the longest time between changes.

What if the battery compartment is stuck or will not open?

Do not force it. Try gently wiggling the cover side to side as you pull, or use a plastic spoon handle to pry instead of a metal tool. If it still will not budge, the plastic may be cracked or the mechanism may be broken — contact Honeywell support or a local HVAC technician for help.

Will changing the battery affect my heating or cooling?

No. The battery powers only the thermostat's display and controls. Your furnace or air conditioner will continue to run on its own power supply. If you turn off the breaker while changing the battery, the system will pause until you turn it back on.

How often do Honeywell thermostat batteries need to be changed?

Most alkaline batteries last one to two years, depending on how often the thermostat switches between heating and cooling. Battery-only models drain faster than hardwired ones. Replace them as soon as you see a low-battery warning rather than waiting for the display to go dark.

What should I do with the old battery?

Take it to a battery recycling program or a retailer that accepts used batteries — many hardware stores and electronics shops have drop-off bins. Do not throw it in the trash, as alkaline batteries can leak chemicals into soil and water.