I accidentally left my Flint in my car overnight earlier this week. It was really cold that night. I think the temp dropped below zero F that night. I brought it in and it didn't want to turn on. I put it on the charger after awhile and it was fine after charging and warming up. Not sure if I did any permanent damage to the battery, but if I did it's my own fault!
I have a mod that does the same thing. The battery just won't work when really cold. But as soon as it warms up it works fine. You should be ok.