The running time will be affected but if the unit stays in his pocket it should be ok.. Most batteries that are lion can handle a -5 temp with out changing much.
I haven't been able to track down anybody who worked on the March of the Penguins movie, but I want to know how much runnning time they got out of the Cantar. It's one thing to be at -5 F, but another when you're in the -40 and lower category... Those batteries probably couldn't have lasted longer than about 30 minutes. I suspect they probably built some special housing of sorts to go around the unit, but still it was friggin' cold out there....
If the original poster gets an official answer, please post it back here. I'm sure most of us would like to know what Edirol and battery manufacturers say about it.
Wayne