What type of batteries does a Honeywell thermostat use?

Most Honeywell programmable thermostats use 2x AA alkaline batteries (RTH2300, RTH6360, RTH6580, RTH7600, RTH8560, TH4110D). The Honeywell T6 Pro uses 3x AAA batteries as backup. The T9 and T10 smart thermostats don't use replaceable batteries — they're powered by the C wire. Always use fresh alkaline batteries (Energizer, Duracell) — rechargeable NiMH batteries are 1.2V vs 1.5V and may cause issues.

How often should I replace Honeywell thermostat batteries?

Replace batteries every 12 months as preventive maintenance, or immediately when you see a low battery warning. Most Honeywell thermostats display a blinking battery icon or "BATT" warning 1-2 months before the batteries die. If you wait until the screen goes blank, you may lose your programmed schedule. Pro tip: replace thermostat batteries when you change your smoke detector batteries.

Will I lose my thermostat settings when I change batteries?

Most modern Honeywell thermostats (2010 and newer) retain their programming in non-volatile memory — your schedule and settings are preserved during battery changes. However, older models may lose the clock time and date. Some RTH models store settings for about 2-3 minutes without power, so change batteries quickly. If settings are lost, you'll need to reprogram the schedule and set the clock.

My Honeywell thermostat shows low battery but the batteries are new. Why?

This usually means: (1) you're using rechargeable batteries (1.2V isn't enough — use 1.5V alkaline), (2) battery contacts are corroded (clean with pencil eraser), (3) you inserted batteries with wrong polarity, or (4) one battery is weaker than the other (replace both, don't mix old and new). In rare cases, the thermostat's voltage detection circuit is faulty and the unit needs replacement.

Can a Honeywell thermostat work without batteries?

It depends on the model. Hardwired models with a C wire (T9, T10, many RTH Wi-Fi models) use batteries only as backup and work fine without them. Battery-only models (most basic RTH series) won't work at all without batteries — they're the sole power source. If your thermostat has both a C wire and battery slot, the batteries provide backup during power outages.

Where is the battery compartment on a Honeywell thermostat?

For most RTH models: pull the thermostat body straight off the wall plate (it snaps on/off) and the battery compartment is on the back or right side. For the T6 Pro: slide the faceplate up and off to reveal the battery slot on the back. For round models (T87): these don't use batteries. For the TH4110D: the battery compartment is accessed by pulling the entire unit off the wall plate.

Battery Guide

Honeywell Thermostat Battery Replacement

Find the right battery type for your model, learn how to replace them in 2 minutes, and fix common battery-related issues.

Last updated: February 2026

Battery Type by Honeywell Model

Model	Battery Type	Access Method
RTH2300	2x AA	Pull off wall plate
RTH6360 / RTH6580	2x AA	Pull off wall plate, battery on right side
RTH7600	2x AA	Pull off wall plate
RTH8560	2x AA	Pull off wall plate
RTH9585	2x AA (backup)	Pull off wall plate
TH4110D1007	2x AA	Pull off wall plate
T6 Pro (TH6320WF)	3x AAA (backup)	Slide faceplate up
T6 Pro (TH6220WF)	3x AAA (backup)	Slide faceplate up
T9 Smart	No batteries (C wire powered)	N/A
T10 Pro Smart	No batteries (C wire powered)	N/A
Round T87 / CT87	No batteries (24V powered)	N/A

Step-by-Step Battery Replacement

Identify your battery type

Check the table above for your specific model. Most Honeywell thermostats use either 2x AA or 3x AAA alkaline batteries. If you can't find your model number, pull the thermostat off the wall — the battery compartment will show the battery size. The model number is printed on the back of the thermostat body or on the wall plate.

Pull the thermostat off the wall plate

Gently pull the thermostat body straight toward you — it's held on by pressure clips or a simple slide mechanism. Don't pull on the wires. For the T6 Pro, slide the unit upward off the wall plate. For older RTH models, pull straight out. Some models have a release tab on the bottom — press it while pulling.

Remove old batteries and check for corrosion

Take out the old batteries and inspect the battery compartment. If you see white or green buildup on the contacts, this is corrosion — clean it with a pencil eraser, cotton swab dipped in white vinegar, or a small piece of fine sandpaper. Dry the compartment completely before inserting new batteries. Corrosion is a common cause of "replaced batteries but still not working" issues.

Insert fresh alkaline batteries

Insert new batteries matching the + and - markings in the compartment. Use only fresh alkaline batteries from the same package (don't mix brands or old/new). We recommend Energizer MAX or Duracell CopperTop. Do NOT use rechargeable batteries (1.2V NiMH) — Honeywell thermostats need the full 1.5V from alkaline cells to function properly.

Reattach the thermostat

Push the thermostat body back onto the wall plate until it clicks. The screen should turn on within 5-10 seconds. If the screen doesn't come on: (1) pull it off and recheck battery polarity, (2) clean the battery contacts again, (3) try a different pair of batteries. If still nothing, the issue may not be the batteries — see our Honeywell troubleshooting guide.

Verify the clock and schedule

After replacing batteries, check that the current time and day are correct. Most modern Honeywell models retain the time, but some older ones reset. If the time is wrong, the programmed schedule will run at the wrong times. Set the correct time and verify the schedule is still programmed by pressing the "Schedule" or "Program" button.

If these steps resolved your issue, your thermostat should now be working correctly.

Pro Tip

Replace thermostat batteries at the same time you replace smoke detector batteries — twice a year when clocks change for daylight saving time. This prevents unexpected blank screens on the hottest or coldest day of the year.

Battery Troubleshooting

Screen still blank after new batteries

Double-check battery polarity (+ and - marks)
Clean battery contacts with pencil eraser — corrosion is invisible at first
Try batteries from a different package (bad batch happens)
Check if the thermostat also needs the C wire for main power (T6 Pro batteries are backup only)
Check the circuit breaker and furnace fuse if hardwired

Low battery warning with new batteries

Confirm you're using alkaline batteries (1.5V), not rechargeable NiMH (1.2V)
Don't mix old and new batteries — replace both at once
Don't mix brands — use the same brand for both/all batteries
Check battery contacts for corrosion or loose springs

Batteries drain faster than expected

Batteries should last 8-12 months. If they die in under 3 months, the thermostat may have an internal short
Wi-Fi models drain backup batteries faster — ensure the C wire is connected for primary power
Very cold houses (below 55°F) can cause batteries to drain faster
Excessive screen brightness or backlight can reduce battery life on some models

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C Wire Guide

When batteries aren't enough

Replacement Cost

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Frequently Asked Questions

Written by

ThermostatFixer Editorial Team

Our team of HVAC enthusiasts and DIY experts creates detailed thermostat troubleshooting guides, wiring diagrams, and repair tips to help homeowners fix common thermostat issues without calling a technician.