My current MKII handles extreme cold reasonably well. At -40F each battery will hold out for 10 or 15 min. or a bit longer as they slowly reach ambient temperature and die. At -50F I can get 3-5 min per battery, enough for an aurora panorama. After re-warming they are able to be used again. I rotate a group of 6 batteries. I have tried tethering an external battery but for a variety of reasons I find it unworkable. I am considering a 1DsMK III for all the obvious reasons but the battery is a real concern. In "normal" cold temps the LI is a great choice but I know it drops off rapidly with regard to power as cold gets to it. Does anyone have a sense of how the battery in the upcoming MKII will handle severe cold in the -40F to -50F ?
