Thanks for reaching out and sorry for the delayed response.
Upon checking on the case id you provided, your thermostat is not holding battery charge but it is charging when plugged in via USB cable. This means that there is no power coming from your HVAC system to the Nest Learning Thermostat so it uses it's internal battery which will eventually deplete after a couple of days. I have a few questions to better understand what's going on:
We haven't heard from you in a while so we'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the Community.