I have a 3rd gen Nest Learning Thermostat. It was working fine for a 1 1/2 years. All of a sudden I see that it shut off. I read the info on web, so I charged and retried, it drained within 8 hours. I connected my old thermostat and both heating and cooling systems work. I reconnected (after charging through USB), the voltage was 3.9 and then few hours later I see it dropped to 3.7 and then later shut down.
I do not have "common" wire. I have connected Rh, Rc, W1, Y1 and G. There are not spare wires.
It is very frustrating to see an expensive unit failing. My 2 year old Nest Thermostat (which has only heating connected) is working fine.
