In a previous post I talked about this box but pics are worth 1000 words. So here are the pix

First the box parts



Then the box with 1/2A sized lipos in it



The ACE hot/cold pack is heated in a microwave oven at full power for about 1 min. It comes out at about 120F. It keeps the batterys above room temperature for over an hour. I have found that lipos perform best when they are at about 100 to120F just before the flight so I actually use this about 9 months of the year here in New Hampshire.  The box could be made larger for larger batteries.

Jim,

Nice job. I have also used packaged hand warmers slipped in my ammo box that I use to store my packs.

Best,                  DennisT