Seems like a good idea but has anyone used one while hunting? Online reviews that I have found are from golfers, college students and soccer moms :)
I googled 'ha warmers' nothing, I don't know what that is. Do you mean hand warmer? For the long haul, good gloves and a warm pocket may be more practical, we had the ones with lighter fluid in the 60s. It seems that every time I remembered my hand warmer, I forgot my matches.
I'm not familiar with the one you posted, but did try this Thermotrek hand warmer last season.
Gets much warmer than the packet type and recharges with usb on computer. Only problem I had with it was it fell apart after about a month. The usb connection in the warmer fell off into the unit and I finally got it apart but could solder the connection back.
I take blood thinners and it was just what I needed so will probably give one another try..maybe super glue the connect for extra strength.
I just looked and this may be a lithium Ion battery.
(http://img.photobucket.com/albums/v71/Iflytrout/Pictures/48010_Elements_Thermotrek_1_zpsguo3zrhv.jpeg)
Oops, yes hand warmers. The unit you showed looks similar to ones I have seen.
We sell those at the archery shop I work at. They are awsome!!!