AC thermostat and batteries?

[60 Deluxe]

I’m so confused now.

Replace the batteries. If it burns through batteries then replace the thermostat or try landing a wire on C as suggested above. I'm not sure how that will work since the transformer puts out something like 20 volts and the batteries only amout to 1 1/2 or 3 volts depending on how they are connected. My tstat gives a low battery message so I cannot access the settings to see if it will even run in that state. It happens so rarely that I haven't given it a lot of thought. I do try to put quality batteries in it.