My M9 will work in cold temperatures, but is erratic. I can make a few frames then the camera shuts down, occasionally making the last frame an unreadable DNG. Can start it up again a few moments later, but it is quite difficult to use when it gets very cold. I've not done a lot of shooting with it in extreme cold, so can't say if this has anything to do with which of my batteries is in the camera. Could give it a test today as it is -21°C here and not expected to warm up at all over the day and maybe even get colder, but I don't much want to be out.