I bought a new 2013 C-Max Energi in late 2013 and bought an extended too. Good thing I did. The C-Max now has some history behind it and it turns out that it is the worst with most problems of all plug-in hybrids. One big problem that is very common has just hit us at 23,000 miles: the 12 volt battery leaks a charge while it is parked. In two days it went from charged to dead (3.05 volts on the multimeter). Ford has no answer or solution. They try to blame it on the driver for being a "low mileage driver" in some cases. Some people have gone through 4 or 5 new batteries because they were told the battery was "bad".... 4 or 5 times. And this vehicle has gone from a cost of $32,000 at purchase, to a value today (in excellent condition) of $15,000.
If you can get an extended warranty, get it! This is new technology and it is far from perfect. I regret buying the thing. In the meantime all I can do is call roadside assistance for a jump start, charge it when I get home, and when the battery doesn't take a charge any longer I can have it towed to a dealership to fix it (new battery is all they'll do), and hope that if everyone with this problem costs Ford money, maybe they will decide to track it down and provide a real solution.