I didn't want to have a bunch of wires to deal with, so they have a battery pack that fits in the cuff. The gloves are thick, so I don't feel much of the actual heat, but they kept my fingers "not cold" while shoveling for about an hour in windy 20F weather. With regular Thinsulate gloves, my fingers would start getting cold after about 5 minutes and be numb in about 20, so I'm happy with 'em!
Hoping to get a commute in this week to see how they do on the road... if I can find a morning or two where it's at least above freezing...