Oct 07, 2013 - 11:00 AM
I had issues with my 12V, but it was related to another issue. I had a short in a wire bundle that was worn by my trunk being opening/closed which caused a high temperature reading in a high voltage battery sensor, causing my fans to go on all the time, even when my car was powered off. This caused the 12V to drain within 8 hours. It took a while to figure this out because it was intermittent, but since it has been repaired, the car has been like new.
I also heard of someone always leaving their keys in the ignition in a standard Fusion, and the 12V draining after sitting for a week. DO NOT LEAVE THE KEYS IN THE IGNITION!!! Apparently this powers up various things and over time, your 12V will drain.
So, while I also did hear of faulty batteries in early C-MAX Energi models, I would have to believe that 12V drain is caused by other issues, faulty components, etc.