It was -10F (-23C) this morning, it's going down to -20F (-29C) this weekend, and I realized that I have a 5 year old battery in my '02 Passat.
The factory battery (Varta, I think) in my '94 Saab dropped stone dead one morning when it was only 2 years old.
I'm suddenly thinking about doing a pre-emptive battery replacement before I'm stuck somewhere.