Hyperion's info says operating temp for the lipo itself should be above 50F (10C). Their suggestion on storage is 37 - 68F (2 - 20C). I read about people storing them in the freezer at much lower temps and they apparently see no immediate downside. I'd worry much lower storage temps could impact ultimate life though. I store mine in a refrig at ~40F. I give them about 2 days to recover when I remove them before trying to charge/use them again.

I doubt these temp ranges are absolutes, but how much tolerance there is before poss impacting your lipos, I don't know.

Hyperion did mention colder temps could cause an overvoltage condition - something to be aware of.