Fly the Team Iceshanty Flag! Iceshanty Proshop
I wear Gerbing heated vest liner, the thinnest one they make. over a tee shirt keeps me warm ice fishing/deer hunting for 8+ hours on low/medium. when you buy one, get a spare set of batteries just in case.
I have the Milwaukee heated vest (and hoodie and jacket), it's great for short trips, small errands or a garage cleaning, but the battery doesn't last long enough for a day of ice fishing imho.