There really is no solution - my 3+ year old battery occasionally fails to hold a charge (or get fully charged) and there is no viable replacement, so my only solution is to manually charge the Nest when it happens or buy a new one. Fortunately 30-45 minutes on the charger is enough to get things behaving, but it's not a very good solution, nor is not having a decent replacement battery good customer service. I realize at least part of the problem is the way my thermostat/furnace wiring is set up - I have no C wire, resulting in my battery only charges when heating or cooling is happening, but it's clear that the battery is not what it once was.
