I usually just take some disposable hand warmers, wrap them around one or two li-pos, and shove them down inside a wool sock. I leave them in my truck until I'm ready to use em. On my 3s 2200mah li-pos, they usually work quite well with this method. They stay warm enough to get your plane moving, and like Max said, the heat they generate is usually enough to sustain them. Good luck bud.