Ok, ill take a look at them, I had some of the small hand warmers yesterday and it did jack as far as staying warm. A heated coat underneath something sounds like it could be good, I need to do some hunting clothes shopping and figure stuff out now that its getting really cold.This is what I got: Gerbing Gyde 7V Torrid Men's Softshell Heated Jacket - Camo
I found it on ebay for half price brand new. I wear an under armour or similar shirt as a base layer, then a merino long sleeve, this jacket in the link, then a camo pull over. For bottoms it's merino long underwear and then thin camo pants. My legs don't get real cold so if it's warmer just the thin pants. The pull over is not a hoodie but has a single front pocket like most hoodies and I use hot hands in there. The mega 18 hour ones are the best. The little 8 hour guys are just enough to keep me on stand but not enough to keep me warm.
The heated jacket is worth $100 to me, I wouldn't want to pay more for how effective I think it is but its also low voltage (7v). If I get a different one I think I'll go 12v if I can find one that fits well enough to hunt in.