The newly replaced batteries in my older house thermostat ( with a mechanical clock) got hot to the touch? Why? I never noticed this before. Is is an issue to worry about? Thanks. MH

I’m ready to save money with a programmable thermostat. I have an old boiler (radiator heat) and a brand new Trane central air conditioner system, installed in January of this year. Is there any advantage to buying a Trane programmable thermostat over another brand thermostat (since my a/c is Trane)? Any disadvantages?
Thanks.