Changing The Batteries - Carrier Comfort Touch-n-Go Owner's Manual

Changing the batteries
Your thermostat is probably powered by the HVAC equipment, but if it isn't, it's
battery powered. You can tell if it's battery powered by checking in Advanced
Programming Options. (See page 37.) If there's no lighting until you touch a button,
it's battery powered. When the thermostat uses electricity, the batteries (if installed)
take over if the electricity goes out. This allows you to monitor the indoor
temperature when there's no electricity.
When powered by batteries, your thermostat's two AA batteries should last about
one year. When your batteries have lost about one-third of their power, a battery
icon shows up on the display in the upper right corner. Two-thirds of it will be
black. As the batteries get weaker, the icon goes down to one bar and then none.
When the battery icon is less than full, you will first see the loss of backlight
function. When the batteries are completely dead, you won't be able to use the
thermostat.