Battery Warmer

This is designed to fit over the battery while on the camera. Inside you insert a few hand warmers and they provide heat to the battery so it will last longer while operating the camera in very cold temperatures. I have tried it out on some cold nights and it worked wonders.
it might need some tweaking to get it to fit perfect depending on what brand batteries you have. Kastar batteries may have some ridges that make it too tight. Sand here and there or shave off some of the design. Whatever works