Dont worry. They write this strange thing just to cover them selves.
I living in the North of Norway and sometimes I operate my 5D in temp. belowe -20'C and it works good. Because I photograph the Northen Lights wintertime, the working temperature is ofte belowe -5 to -10 'C.
My earlier cameras was 300d/Rebel, 20D and now I have a 5D and I have never have some problem with them in cold temperature. Well, there was one time we was out for 5 hours in -17'C. The camera become a bit slow at the end.
I have always used BP-511A battery, not BP-511. 511A has 1390mAh and this is actually a big differense from 511's less mAh.
There are some small triks you have to remember to make your low-temp photographing sucessful:
- Bring your battery in your pocket to keep it warm. Every time you stop photographing, remove the battery from the camera and put it in your pocket. always. even for small breakes
- Bring extra battery!!
- But, if you want to keep the battery in your camera all the time, remember to switch off the camera. Dont leave it in standby mode. Every small mAh counts in this conditions
- After you've taken your camera outdoor, keep it there until your're finished or keep in in you camerabag. Do not bring the camera indoor again for a short time because of the dew and moisture.
- Always put your camera in the bag before taken it indoor after your photo session. This allow the camera to be heated up slowly again.
Canon is the most sold cameratype in Norway and I dont think the average temp is over 10'C in this country, year over.