I remember using my battery-powered socks for cold sports events. They had two large size D batteries on each sock. There was a copper wire all the way down to the toes. They were originally for snow skiing. They worked really well. Your feet were not necessarily ‘warm’ but the toes did not lose circulation.
I had a pair like that. Had to pull one of the batteries out every so often or it felt like my toes were roasting!
I use my battery socks here at home on really cold days. They use LiPO batteries these days. I’m not impressed, though. I was looking for nice gentle uniform heat all around my feet and ankle, but it’s more spotty and localized. I think mine were mainly made for hunting.