I just killed my 2013 FFE (inadvertently) by getting out at my office in the morning without turning it off. I thought I had turned it off, but that didn't work because I wasn't in Park. The car doubtless beeped at me but I was in a hurry and ignored the signal. By the end of the afternoon, the car was completely dead because the 12V battery was depleted by the various controls and a seat heater that didn't know to turn off. I jumped it with a portable miniature lead-acid battery we keep for this purpose, and after 2 minutes' 12V charge it was fine. A good lesson in making sure, when you get out of your car, that it's REALLY off.
However, I'm puzzled that the nearly-full traction battery didn't use its DC-DC converter to recharge the 12V battery so the car would start. I seem to recall another post's saying that this works only when the car is being recharged. I don't see the rationale for that requirement. Of course the designers don't want to run out of traction energy, but it's unusable anyway if the 12V battery is dead. Maybe Ford could change the software so that if the 12V battery has seen a long steady load but no driving activity, it could hypothesize that the driver simply forgot to turn off the car and could recharge the 12V battery from the traction battery even if the car isn't plugged in.