I've been looking at the jackets from DEWBU, thinking of getting one for Melissa. Some days on the river she's pretty cold by the time we pull the boat out, even with multiple layers so was thinking one of these may help her stay a bit warmer.
My daughter and several other swear by them at the barn and winter horse work. They like the vest and you can adjust temp and layers according. All the ones I have seen use a simple battery pack in a dedicated pocket (just a USB power pack like for a phone) been thinking of trying one in the duck blind