I've got some battery powered long underwear that I use bowhunting during November or when it's really cold and the wind's a blowin. I'll have to say that they awesome! I can sit in my stand all day and just adjust the temp with a thermostat. The batteries are kind of bulky but when you get to your stand it's not bad. My dad just take a 12v car battery and puts at the bottom of his stand and runs a cord up to his suit that has a 12v cigarette lighter plug on the end.
These suits were made for motorcycle riders but I've started to use them bowhunting and it's the cats meow.
Does any of you guys use them?