Hello, forum heads

It's pretty cold here in Belarus, and seems like my PRS-505 doesn't like it very much

Every time I go out and take it with me (I'm usually carrying it in my back pack) - it discharges a lot while being on cold, even in back pack. I know that Li-Ion batteries are no-good when it's cold outside...
I tried to use my scarf to protect the reader, but almost no effect here. Does anyone know, maybe I could buy a special cover or something like that to protect the device?
Thanks in advance!
BeTePoK