There must be two generations of Nest Hello (aside from Google version) - one with a 'plain' battery. The other generation (mine/yours) have a battery wrapped with a ribbon heater (I found a Reddit black hole - I guess this is called a Kapton heater). FYI, the battery is the white 3-wire and the heater is the black 2-wire. I guess Lithium batteries do not charge well in cold weather, hence the heater.

So, I painstakingly tried to unwrap the heater (it's got tape and layers of adhesive around the battery), but it eventually broke. I pulled out the heater's two wires (black/red) from the connector and tossed it. I replaced the battery as per usual and it's working fine without the heater. I'm in Chicago and it gets %#*@ cold, so I'm hoping there won't be performance issues this winter.

I searched for a replacment battery with the heater, but no luck. And I couldn't find a kapton heater replacement either. These must be very specific Nest/OEM parts that are not readily available to the public.

Good luck!