I’ve been using a combo hand warmer + battery charger + light in the winter when camping.

The one I have is similar to this but under the “Kozy” brand name:

https://www.amazon.com/Outdoors-Way...y+charger&qid=1631446956&sr=8-16

The hand warmer function is great and can warm the phone itself when you forget to keep it within an inner chest pocket.

Last edited by alukban; 09/12/21.