Replacing the Battery in a Honeywell Thermostat. Follow these six steps to replace the battery in a Honeywell thermostat. Step 1: Switch Off the Thermostat. 2 AA/AAA if 5000) and below for where the batteries are typically located. Replace all of them unless you are willing to test each battery's charge, which should not exceed 1.1-1.2.. Battery Type Location Model Example; 1000 Series: 2 AAA batteries: Under the cover plate: PRO 1000 Vertical Non-Programmable Thermostat: 2000 Series:. Table: Honeywell Thermostat Battery Replacement Comparison. Model Battery Type Estimated Battery Life How to Confirm Battery Level Additional Features; Honeywell RTH9585: AA:
Honeywell Thermostat: Battery Type: Number of Batteries: Battery Location: 1000 Series: AAA: 2: Under the cover plate: 2000 Series: AAA: 2: Under the cover plate: 3000 Series : AA: 2:. Some control panel faceplates require removing a small screw located under the faceplate to access the batteries... Step-by-Step Guide: How to Change Honeywell Thermostat Battery. Now, let's get into the nitty-gritty of replacing the battery: 1. Locate the Battery Compartment: On most Honeywell thermostats, the battery compartment is located on the bottom or side of the thermostat. You might find a small cover or a latch that needs to be released to access the compartment.