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Honeywell Home thermostats use different battery sizes depending on the model. Official examples include two AA batteries in the FocusPRO P200 and N100, AAA alkaline batteries in the FocusPRO 5000 TH5110D, and AA alkaline batteries in the TH5320U and TH5220D. Check the model number and its specific manual before buying batteries; some wired thermostats use them only for backup power.
Which battery size does your Honeywell thermostat use?
There is no single battery size for every Honeywell Home thermostat. The examples below are documented for these specific models; they are not a complete compatibility list.
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| Model | Documented battery requirement | Power note |
|---|---|---|
| FocusPRO P200 | Two AA batteries | The manual calls for fresh AA batteries. Resideo product page and P200 manual |
| FocusPRO N100 | Two AA batteries | See the model documentation. Resideo product page |
| FocusPRO 5000 TH5110D | AAA alkaline batteries | Battery backup is optional when the thermostat is wired for AC power. FocusPRO 5000 manual |
| FocusPRO 5000 TH5320U and TH5220D | AA alkaline batteries | Battery backup is optional when the thermostat is wired for AC power. FocusPRO 5000 manual |
| FocusPRO TH6320R | Two fresh AA alkaline batteries | Its low-battery warning flashes about two months before depletion, according to its manual. TH6320R manual |
How to confirm the right batteries
- Find the model number. Check the label on the thermostat or its packaging. If the thermostat is mounted on a wall plate, consult its documentation before removing it to look for a label.
- Open the matching user guide. Use the model number to find the corresponding Honeywell Home or Resideo manual. Confirm battery size, count, chemistry, and polarity; do not assume another model in the same series uses the same cells.
- Check whether batteries are primary or backup power. The FocusPRO 5000 manual says batteries are optional for backup if the thermostat was wired to run on AC power when installed. In that setup, replacing batteries may not be necessary for normal operation.
- Follow the model’s replacement procedure. The P200 manual instructs owners to remove the thermostat from its mount, insert fresh AA batteries as shown, and reattach it. Other models may have different removal and battery-access instructions.
What to do when the low-battery warning appears
Replace the batteries with the exact type and number specified in the manual for your model, observing the marked polarity. The FocusPRO TH6320R manual says its low-battery warning flashes about two months before depletion; that timing applies to that model and should not be treated as a general warning period for all Honeywell thermostats.
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If the thermostat is wired for AC and batteries are only backup, check the model manual to determine whether the warning reflects backup batteries that need replacement. If the correct batteries are installed but the warning remains, verify polarity and that the thermostat is seated correctly, then consult the model’s troubleshooting instructions.
Quick Recap
Bestseller No. 5
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Honeywell Home X2P Programmable Thermostat, White
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For Nest Thermostat Battery 3rd Generation: TL284443 Battery Replacement
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HW CR123A 3V Lithium Battery 6-Pack, 1700mAh High Capacity 123 Batteries
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For Nest Thermostat Battery 3rd Generation: TL284443 Battery Replacement
- 【TL284443 Battery Replacement】: Widely compatible with Nest Learning Thermostat 3rd Generation gen 3 A0013 T3007ES, part number: TL284443
- 【650mAh High capacity Battery】: Battery for Nest thermostat is made of high quality lithium polymer material, with a capacity of up to 650 mAh, which can provide you with safe and efficient charging
- 【Battery for Nest Thermostat gen 3】: Battery type: Li-Polymer, capacity: 650 mAh / 2.1 Wh, voltage: 3.7 V, weight: 12.1 g, size: 1.97 x 1.7 x 0.78 inch
- 【Battery for Nest Thermostat 3rd Generation】: TL284443 battery has no memory effect, with over-charging, over-discharging, overheating, over-current and short-circuit protection
- 【Battery for Nest Thermostat A0013 T3007ES】: New battery for Nest 3rd generation thermostat achieve optimal performance and longevity only after 3 to 5 full charge/discharge cycles
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