I was wondering if it's ok to keep extra batteries warm by using those instant hand warmers, that you smash and they become warm for 4 hours. What I intend to do is wrap them around the extra batteries with rubberbands while outside in the cold. Seems most people complain that the cold reduces the charge in batteries. Any thoughts on this or other ways to keep them warm? Thanks again

I was wondering if it's ok to keep extra batteries warm by using those instant hand warmers, that you smash and they become warm for 4 hours. What I intend to do is wrap them around the extra batteries with rubberbands while outside in the cold. Seems most people complain that the cold reduces the charge in batteries. Any thoughts on this or other ways to keep them warm? Thanks again