I race a big local race this weekend and it was about 50 deg. outside. I put a Lipo in my inside coat pocket after I charged it for about an hour. When I put it in my truck it was body heat warm, which was alot warmer than the outside temp. The car had loads more punch and speed down the straight. SMC has posted that the batteries take a better charge when about 140 deg. I am going to pick up a heating pad for the next race. I hear tire warmers work well also but not as nice to sit on when your not racing.