Or you could wear some long johns, a layer or two and a jacket...take something off as you warm up. Totally pre 21st century but it works. No 'lectricity required. Won't ever fail either. Just sayin...
I have the heated vest and it works great but I am looking for something for the legs now. I have the long johns and the latest thermal pants but I am wore slap out with that after a day of riding and not being able to bend my legs. So I am looking for something else that is warm and easy to wear. (Comfortable to wear)