My wife refuses to let me pull the kids in the trailer once it gets below -15C ambient (she's from the Southern US... and has Views on these things). This morning was -13, but the battery (relatively new less than a month of usage on it) held it's charge, which surprised me a bit. Last winter I wouldn't get more than 10 minutes of mplayer on a full charge before it got "critically low" once it dipped below -15 or so. -18 tomorrow (-25 with windchill, at least for those standing still)... there will be no photography.