There was a heated-wear store in Olympia, in the past.
I think Milwaukee or other major manufacturer makes other battery heated clothing.
Some rocks out in boiling water, then in jacket pockets is a start for a hand warmer.
I hear people used to have baked potatoes for horse riding, before cars, providing a hand warmer and snack.
The Costco ones are under $80. Costco is meant to be good quality and standing behind their products.
The first pair was from a Chinese company and were good until the batteries crapped out.