Naturally Aspirated wrote in post #9015883
i lived in korea for 5 years, and it doesnt get that cold...
Agree. I spend a lot of time in Korea and like in MN. MN is way colder. Now, North Korea is probably a bit colder.
Either camera works fine in the cold. The advantage to the 5D is that the batteries are super cheap and you can easily carry lots of them (keep them inside your jacket). The 1Dmk3 has a better battery but it too will lose a lot of capacity as it gets cold and the batteries are more expensive (a lot more expensive). For what it's worth, I've routinely shot my 5D at 0-10F and even to -20F once (Fahrenheit).
Both batteries are Li-ion so they will behave similarily in the cold. The benefit is that the 1Dmk3 battery has much more capacity and is a bigger thermal mass so it will (a) tolerate losing capacity better and (b) take longer to cool down. The trick is to never let the batteries stay in the camera long enough to get really cold.
Here in MN, some photogs will take those little heating packets that you can put in your gloves and tape them over the battery compartment with gaffers tape. I don't do that, it's a pain in the neck. I just keep two batteries - one in my coat, one in the camera - and swap them before they get totally cold soaked (keep them warm). You should not freeze either battery.
J.