I'm from NC pretty much and moved to MN for 1yr and experience the great artic mid-west. I know it's a common practice to keep a battery charger/warmer on your battery. I'm sure there was more to it besides just a battery charger but I forgot it because I moved the hell out of MN after that winter, now back down in the 2 month winters of NC =D.
Good luck, if this doesnt help go to a forum in some winter-wonderland and the locals there should know what to do after generations of trying to help a car survive passed 100k. Between the frozen engine/battery water problem and the rust problem from the salt on the roads, I'd say you need all the luck and help you can get.