Had a bit of a scare with my C-Max during one of my dead battery occurrences.
The dealer recommend I tow the car to them, without jumping the car. So, after much hassle (ex: the tow truck didn't fit into my driveway; the shift lock release isn't where the manual says it is), we managed to load it onto a flatbed and off to the dealer we went.
Got it to the dealer and it was time to unload it from the flatbed. Stepped on the brakes to gradually ease it off the flatbed and released the e-brake - the regular brakes don't work! Fortunately we were able to grab the e-brake before my rapidly-accelerating car slammed into the car behind the flatbed. *WHEW*
So... if your 12v battery is dead, be forewarned - the regular brakes will only work once. After you apply the brakes once, you'll only be able to use the e-brake. Seems like a bit of a design / safety flaw to me.