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It can be used with a 2 wire system, as that is what mine has. Just a red and a white or black and white depending on your set up. Mine have stayed charged at over the 3.7 and seem to gain a little more with use. I have 5 of these set up, and they usually range around the 3.8 charge level. Check out the YouTube channel One Hour Smart Home. The guy is super knowledgeable and was a great resource when i was researching these thermostats to see if it would work with my system.
Sorry, there was a problem. Please try again later.I can tell you that I had this thermostat run on a 4 wire system for almost 5 years before it just stopped working recently. When I bought the replacement of this same model, my 4 wire system suddenly wouldn't work as the thermostat was receiving an issue from the furnace, indicating I needed power (C-wire). I don't know what changed....maybe it was a software update? Or I was just lucky for that entire time and the thermostat was receiving enough of a trickle charge that it lasted that long. What I would recommend is if you have the 4 wire system and need to keep it, do yourself a favor and google "c wire adapter nest thermostat". There are plenty of results...just be sure this adapter is compatible with this thermostat. If you can run this wire up through the wall, great. If not, you'll have a wire showing that runs to a power source. I was fortunate enough to have a furnace with a C-wire on the board so I was able to run a new 5 wire and not need this adapter, but it's certainly an option if needed. Best of luck to you.
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