Damian, In addition to the battery drain and condensation issues, be prepaired for "Err 99" codes if the camera itself gets to cold. I have had this problem several times when shooting with the 50D and once while shooting with the 7D in sub freezing temperatures. I found that just wrapping a bath towel around your camera helps as well as frequent trips to a non-humidified heated area such as a car or truck.


Hope this helps,


Bob