Anecdotal evidence only:
Visiting Urbana IL several winters ago, I left the house with my phone at 100% charge. Â Being a lifelong Floridian, I put the phone in my front pants pocket as usual. Â The high that day was 16F. Â Within 3 hrs the battery was at 15%…in my pocket…unused. Â My wife and daughter’s phones, in their purses, were dead. Â I suspect the little bit of warmth my thigh provided accounted for the difference.
Granted, this experience with the battery in the iPhone may or may not be applicable to PBCs, but I suspect it could. Â I always carry my PBC buried deep within my clothing layers when temperatures are below 30F.