My situation is similar. It worked fine until I added ac (along with a
new furnace). Then it would require new batteries every 2 months. I
turned off the proximity sensor thinking it was the drain but I'm still
changing batteries. 4 times since Febru...
My issue is different. I have a C wire. I thought the proximity
detection was draining the batteries as it would come on many times a
day due to its location. Disabling the auto temp display seems to be
working but I miss seeing the temp when I walk ...