How to Replace a Thermostat Battery

If you have a programmable thermostat, chances are good that it has a battery. Like any battery, the one in your thermostat must be replaced regularly to keep your thermostat–and heating and cooling system–operating correctly. When you notice your furnace or air conditioner acting strangely, one of the first and simplest things you should try is changing the battery in your thermostat.

The location of the battery will vary a bit by manufacturer but here is a pretty good guide to finding and changing the battery yourself.

http://www.ehow.com/how_5711427_replace-thermostat-battery.html