How often should I replace the batteries in my TH5110D thermostat?
Batteries should be replaced once a year, or before leaving home for more than a month. The 'Replace Battery' warning will begin flashing approximately two months before the batteries are fully depleted, so you should install fresh batteries as soon as the warning appears. (Page 10)
From the official Honeywell TH5110D Home Programmable Thermostat manual, page 10
Have a follow-up question?
Answers from the official manual.
Common questions