Block heaters in cars are not effective in extremely cold temperatures. They keep the oil warm, but the battery still gets too cold to crank. In college, I used to remove my car battery from my car and store it on my kitchen floor at night so I could start the car in the morning.
Cameras will suffer similar issues. Lithium Ion batteries are only rated down to -20degC. Below that, the internal impedance of the battery rapidly increases as temperature decreases, and you get extremely shortened battery life. I once tested a product I designed, that normally works for 24 hours, and got only 2.5 hours from it at -40degC.
In my anecdotal experience, a standard compact camera battery, also Li Ion, works quite poorly on a ski slope at -5 to -10C. Battery life was less than a third of usual for several days running, despite a full charge each night.
as a side note, you can put the battery back in your pocket with a hand warmer, and it comes back to life. I tend to do this on cold days with my phone also, so that the batteries stay warm in case I need to use them.
Cameras will suffer similar issues. Lithium Ion batteries are only rated down to -20degC. Below that, the internal impedance of the battery rapidly increases as temperature decreases, and you get extremely shortened battery life. I once tested a product I designed, that normally works for 24 hours, and got only 2.5 hours from it at -40degC.