How to Replace Battery in Honeywell Thermostat

Honeywell thermostats use AA or AAA batteries (two or three depending on model) or sometimes no batteries if hardwired. Replace yearly or when Low Batt appears (about 60 days warning). Battery access varies by series: many slide or remove the cover plate; 1000–4000 series use batteries under the cover, 5000–6000 use a battery compartment, 8000 and Lyric Round use AAA. To replace: power off, remove cover/compartment, swap batteries with correct polarity, reattach, and restore power. If it won’t power on, check cover seating, battery orientation, battery health, or perform a breaker reset.