Nest 3rd Gen Learning Thermostat Not Maintaining Battery Charge

[hij2001]

I have one of these devices for each of my two HVAC systems and they have been working fine for over 8 years.  Recently the devices started going offline occasionally, apparently due to the battery charge falling below 3.7 volts.  These are both 4 wire heating/cooling systems with no C wire, and no easy way to add one.  The batteries are normally 3.8-3.9 volts. 

We are now in early spring so there are more times when the heat is not running while in heat mode, but my assumption is that the Nest batteries would charge when the system is off and the power circuit is open, which shouldn't create a problem.  Is this correct?

Why has this now become an issue, and what can be done to resolve it?

Thanks and regards,

Howard

[ByronP]

Hi hij2001,

Thank you for posting. I understand this can be frustrating when your Nest thermostat is offline. Help's here.

For this concern, you will need to charge your Nest thermostat into a direct wall outlet with a micro USB port cable for at least 2 hours to get the battery fully charged. Here is a good article you can check and review for the Nest thermostat USB port.

Let me know if you need more assistance.

Regards,

Byron

[hij2001]

Byron -

Thanks for the suggestion, though it's one I've seen and am not enthusiastic about using.  The reality is that this is an occasional problem that resolves itself after a few hours.  It's just an annoyance and suggests that the design could be better.  

Do you know the answer to the question of whether the battery charges when the HVAC circuit is open (not running) as I would expect, or only when it runs as I've read elsewhere?

Thanks and regards,

Howard

[ByronP]

Hi hij2001,

Thank you for posting.

I'm sorry that the suggestions didn't meet your expectations. I understand how frustrating it is, especially when it occasionally happens. Feedback will be appreciated to improve the device in future updates.

For your concern, some advanced HVAC systems might have backup batteries that kick in during a power outage. It's important to consult your HVAC system's manual or contact a qualified technician for specific details about your system's battery usage (if any).

Regards,

Byron