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I just changed the 12 volt battery on my '13 C-Max for the first time. It was a little bit of a challenge due to no mechanical latch on the back hatch door, but it worked out. The dealer has suggested that I bring the car in to have the computer reset (1/2 hour labor). I understand that some high end cars do require that the onboard computers be synced with an individual battery, but is that really necessary on a C-Max? What are the risk if I don't do that?

The 2nd replaced, about a year and a half ago, 12V battery on my CMAX is probably not getting charged even after driving on highway for 50mins to 1hour recenlty: 01/20/2015 11:15AM, after parked the car for 3 hours after hi-way driving 1hour, turned the key to ignition postion 1 to get the radio playing. After 3mins, the radio shutoff, turned the key to ignition postion 3, the "low battery..." message appeared. Turned the car off, and turned the key to postion 1 again, 1 to 2 minus later the radio turned off again. Turned the car on, the "low battery" appeared again. This time I left the key at position 3 for 10mins, hopefully the 12V get charge. 01/21/2015 7:40AM, right after hi-way driving for about 50mins, parked the car, removed the key, radio still playing (have not open the door yet). After 1min, the "low battery" appeared but the screen immediately shutoff. Turned the key to position 3, and there it was the "low battery" appeared again. For each time, I got into and looked at the ET screen for the 12V voltage. If key was at postion 2, the 12V had 12.4Volt constantly. And when I turned the key to postion 3, it showed between 14.3 and 14.4 (flickering between those 14.3 and 14.4). I could have radio on for 20mins or more when key is at postion 1 or 10mins when the key is taken out before I open the driver door. The "low battery" happened from time to time before but never in twice in a row like the above. There were times I saw the "low battery" message and the radio was auto-shutoff. But immediately after that, took out the key, turned the key to position 3 and back to position 1: no "low battery" for 20mins or more until I shut the car off and opened the door. There were also times I saw the "low battery" message on the previous days. And after driving 1 to 2 hours, parked the car for 3 to 4 hour, and then the key to postion 1 and the radio play for 50mins or more before I turned off the car and locked the car. It is probably whatever computer component controlling the 12V battery charging or reading has gone haywire. Or it has always been like this, I do not know. Or the 12V battery is in need of another replacement, but then that replacement get no charging as it is always supposed to. Or another problem adding to the unknown phanthom discharge that still not sovled by Ford.

Wife picked up new C-Max on 3 Nov. On 6 Nov went to start and totally dead. Called Ford Service who sent someone to jump start it. I did not wish to touch it as so new and it being a Hybrid. On 14 Nov while wife was driving the brake warning lights lite up. She pulled off road and shut down car and called home. When restarted all seemed ok, no warning lights or such so told her probably a hiccup and keep an eye on it. I drove and could not recreate. Next day did again and she called and explained problem. I called the Ford Dealer in Knoxville, TN who said to bring in the next day, the15th. I checked car the next morning and got same brake warnings on both displays, left and right side. Driving to dealer brake warnings again and car stayed in gas mode, no EV. Dealer put on computer and said would have to keep for up to a week depending upon if parts needed to be ordered. Wife unhappy. First car that broke in 20 yrs. Traded reliable Honda Accord. Dealer did furnish a loaner but she is concerned about reliability.