Hello,

When my furnace turns on the red light on the thermostat will turn on. The following will happen some on and off while it is running: the red light will turn off, the "battery" signal will come on, and the screen will start to fade. Sometimes the fading will cause the temperature setting to reset or clear. Does this sound the thermostat or transformer?

Thanks for any help

Battery in thermostat or probably thermostat. Check for 24 volts at transformer.

If you have a wire going to C(common) and R(24v) on your thermostat its not the battery. Your thermostat is using the transformer to power it. You say the red light is on when its acting up. I assume you have a heatpump. You may have a drop in voltage when the strips kick in(loose or burnt wire,wire trying to go to ground or bad breaker) or you may have a slight ground on the 24v side of the transformer.