In my 2009 Ford Edge the dealership had no idea what the problem was after the car being in the shop several times. Finally I told them to keep the car until the problem is figured out. They contacted Ford and after 2 or 3 days Ford got back to the dealership and recommended replacing the battery junction box because it can go bad and cause irregular voltage problems. This was replaced, of course out of warranty, and I have had no problems since. I do not remember the exact cost but somewhere between $200 and $400 for the battery junction box and installation. The battery Junction box is where all the fuses are located in the engine compartment above the drivers side front tire area. As usual Ford hasn't heard of any other problems like this but for some reason knew what would fix the problem.