I was able to solve this by installing a C wire 24 V power adapter from
Amazon for $20. 24Volt Power Adapter/Transformer,C-Wire Adapter
Thermostat，Compatible with Honeywell ,Ecobee,Nest and Sensi Smart WiFi
Thermostat Pro(25Foot /7.6M Cable)
https://...
So after wasting a lot of time troubleshooting this issue, the bottom
line is Nest thermostat now requires a C wire to operate, which it
didn’t when it was a Nest product. Google changed this with their latest
software update. Replacing the battery w...
I just reset my 3rd gen Nest to factory defaults, disabled Wi-Fi and
turned it to essentially a dumb thermostat just to I can keep my furnace
running on a 15 degree day. If I knew google was going to buy Nest I
would not have bought this thermostat.
Same issue here with third gen nest , worked fine with no C wire for
almost 4 years and now the battery won’t charge. I wonder if this is a
software issue causing the battery to drain.?
