lithium AA batteries inthe BG-E2n ?
I have never really tested or used AA lithium batteries. I would use them just for real emergencies because they keep their capacity for years - end they are there when you urgently need something...
A much more economic way is 2-4 "normal" batteries of your camera in a warm pocket ( AS ALREADY recommended ) . Voltage drops in cold - but the capacity does not disappear. You just have to warm up the battery again in your pocket.
Also charged Sanyo Eneloop AA batteries can be stored for 6-12 months without loosing much power and they are said to last much longer in cold - it is cheap to test a set of them too. And they can be recharged 500-1000 times .
Lithium AA batteries are quite expensive...
SLR photography for 40 years
60°15´N 24°03´ E