How to Change the Battery in a Honeywell Thermostat (Every Model)

If you want to know how to change the battery in a Honeywell thermostat, first you need to find out which kind you have. On most models, you pull the thermostat off the wall and the batteries are on the back. On others, a small battery holder comes out of the top while the thermostat stays on the wall. And most Wi-Fi models don’t have batteries at all.

This guide covers each model family, with the battery type and the steps from Honeywell’s own manuals. It only takes a couple of minutes and you don’t need tools.

Quick Answer

• Most models (T1 Pro, T4 Pro, T6 Pro, X1N, X2P, RTH6360, RTH7600): pull the thermostat straight off its wall plate, replace the two AA batteries on the back and push it back on.
• FocusPRO 5000 and 6000, RTH6350 and RTH6450: press down on the battery holder at the top of the thermostat, pull it out, replace the AA batteries and put the holder back.
• RTH2300, RTH221, RTH111 and PRO 1000: set the system switch to Off, pull the thermostat off from the bottom and replace the two AAA batteries.
• Wi-Fi and smart models (T5, T6 Pro Smart, T9, T10, X2S, X7S, X8S): they don’t have batteries. They run on the C wire.
• Use new alkaline batteries. Honeywell says rechargeable and lithium batteries don’t work properly in its thermostats.

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Which Honeywell Thermostats Have Batteries

There are three designs, and the Honeywell thermostat battery is in a different place on each one:

• Batteries on the back. This is the most common design. You pull the thermostat off its wall plate to reach them.
• A battery holder. On the FocusPRO 5000 and 6000 and the RTH6350 and RTH6450, the batteries are in a small holder at the top of the thermostat. It comes out while the thermostat stays on the wall.
• Without batteries. Honeywell’s Wi-Fi and smart thermostats run on 24-volt power from your heating and cooling system, through the C wire. Our C-wire adapter guide explains what that wire does.

If you’re not sure which one you have, look for the model number. It’s printed on the back of the thermostat (on the RTH6350 and RTH6450, it’s on the battery holder) and it starts with letters like T, TH or RTH.

On some models, the batteries are only a backup. Honeywell’s manuals for the T4 Pro, the T6 Pro and the FocusPRO say that batteries are optional when the thermostat is wired to run on power from the system. On other models you always need them. The manuals for the X1N, X2P and RTH6360 say the C wire doesn’t power the display, and the RTH6350, RTH6450 and RTH111 only run on batteries.

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Honeywell Thermostat Battery Replacement by Model

Find your model in the table, then read the steps for it below.

Model	Batteries	Where they are
T1 Pro, T4 Pro, T6 Pro	2 AA	On the back
X1N, X2P	2 AA	On the back
FocusPRO N100, FocusPRO P200	AA	On the back
RTH6360, RTH7600	2 AA	On the back
PRO 3000, PRO 4000	AA	On the back
FocusPRO 5000, FocusPRO 6000	AA (AAA on the TH5110D)	Battery holder
RTH6350, RTH6450	2 AA	Battery holder
RTH2300, RTH221, RTH111, PRO 1000	2 AAA	On the back
RTH8500 and VisionPRO 8000 (models without Wi-Fi)	3 AAA	On the back
Round Smart (Lyric Round)	1 AAA lithium (backup)	On the base, behind the thermostat
Wi-Fi touchscreen RTH8580WF	Coin cell (for the clock only)	Inside the back
T5, T5+, T6 Pro Smart, T9, T10, X2S, X7S, X8S, RTH6580WF, RTH9580WF	None	They run on the C wire

Models With the Batteries on the Back

The wires are connected to the wall plate, not to the thermostat, so you won’t touch them.

1. Hold the thermostat by its edges and pull it off the wall plate. On the T1 Pro and T4 Pro, Honeywell says to press it gently first to loosen it. On the RTH and PRO models, pull from the bottom.
2. Turn it over and take out the old batteries.
3. Put in new alkaline batteries, following the + and – marks.
4. Line the thermostat up with the wall plate and push it gently until it snaps into place.

On the T4 Pro and T6 Pro, you won’t have to set the time and day again if the new batteries go in within two minutes.

Models With a Battery Holder

On the FocusPRO 5000, the FocusPRO 6000, the RTH6350 and the RTH6450, the thermostat stays on the wall:

1. Press down on the battery holder at the top of the thermostat and pull it out.
2. Replace the batteries. Most of these models take AA batteries, and the FocusPRO TH5110D takes AAA.
3. Push the holder back into the thermostat.

The two-minute rule for the time and day applies to the FocusPRO 6000, the RTH6350 and the RTH6450 too.

Basic Models With AAA Batteries

The RTH2300, RTH221, RTH111 and PRO 1000 need one extra step. Honeywell’s manuals say to set the System switch to Off before you remove the batteries. Otherwise, the heating or cooling could stay on while the batteries are out.

After that, pull the thermostat off the wall plate from the bottom, turn it over, replace the two AAA batteries and put it back. On the RTH2300 and RTH221, you’ll have to set the clock and the day again. Your schedule stays.

Smart and Wi-Fi Models

The T5, T5+, T6 Pro Smart, T9, T10, X2S, X7S and X8S don’t have batteries to change. If one of them shows a blank screen, the problem is the power from your system, and our Honeywell thermostat troubleshooting guide explains what to check.

There are two exceptions:

• Wi-Fi touchscreen RTH8580WF: it has a coin cell battery inside the back. Honeywell says it only keeps the time and date during a power outage and doesn’t power the thermostat.
• Round Smart (Lyric Round): it has one AAA lithium battery for backup. Pull the thermostat straight off its base, replace the battery following the polarity marks on the base and push the thermostat back on.

The wireless room sensors for the T9, T10 and X8S take two AAA batteries. On the T9 and T10 sensors, you remove the cover, replace the batteries and snap the cover back on. The sensor connects to the thermostat again after a few seconds.

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What the Low Battery Warning Means

A Honeywell thermostat low battery warning looks different on each model:

• T1 Pro, T4 Pro and T6 Pro: a battery icon. The T4 Pro and T6 Pro also show BATT, and the T6 Pro lists it as alert 405 (low) or 407 (critically low).
• X1N and X2P: alert 405, then alert 407.
• FocusPRO, RTH6350 and RTH6450: REPLACE BATTERY flashes on the screen.
• RTH2300, RTH221, RTH111, RTH7600 and RTH8500: Lo Batt flashes on the screen.

According to Honeywell’s manuals, the warning appears about two months before the batteries run out on most models, and about 30 days before on the RTH7600 and RTH8500. Honeywell says to replace the batteries immediately when you see it.

If you wait, the thermostat starts to save power. On the T6 Pro, the screen light turns off when the batteries are very low. When they’re critically low, the screen only shows BATT and the two warning icons. After that the screen goes blank, and a thermostat that only runs on batteries can’t control your heating or cooling anymore.

You don’t have to wait for the warning. Honeywell’s manuals say to replace the batteries once a year, or before you leave home for more than a month.

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Which Batteries to Use

Use new alkaline batteries, and replace all of them at the same time. Honeywell’s manuals specify alkaline, and its support site says that rechargeable or lithium batteries won’t work properly in the thermostat. The only exception in this guide is the Round Smart, which takes a lithium AAA.

In most communities, used alkaline batteries can go in the household trash, but the EPA recommends recycling used batteries when you can.

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If the Thermostat Doesn’t Work After New Batteries

If the thermostat doesn’t turn on after a Honeywell thermostat battery replacement, start with these checks:

1. Check the batteries. They should be new, alkaline and placed according to the + and – marks.
2. Push the thermostat onto the wall plate again. It has to snap into place to connect to the wires.
3. Set the time and day if they were erased. The other settings are stored in permanent memory, so your schedule is still there.

If the screen stays blank, the next step depends on the model. Honeywell says the RTH6350, RTH6450 and RTH111 only run on batteries, so if new batteries don’t turn one of them on, it needs to be replaced. Our guide to the best Honeywell thermostats covers the current models. If your thermostat is also wired to a C wire, check the breaker and the power switch at the furnace before you replace anything.

You may have read that putting the batteries in backwards for 30 seconds clears a low battery message. Honeywell does describe this step, but only for four older models (the CT3200, CT3300, T8112 and T8132), when the LOW BAT message stays on after you install new batteries. We don’t recommend it on any other model.

If the thermostat turns on but doesn’t respond, our guide on how to reset a Honeywell thermostat has the restart and reset steps for each model.

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The Bottom Line

Changing a Honeywell thermostat battery is a quick job when you know which design you have. Most models come off the wall plate and have two AA batteries on the back. The FocusPRO and the RTH6350 have a battery holder at the top, and the smart models don’t have batteries. Use new alkaline batteries, replace them once a year, and don’t ignore the warning: on most models you have about two months before the screen goes blank.