New 2017 MKZ - 9800 mi.
Last week had the "System Off to Save Battery" thing. First would not start, then finally did.
Yesterday same thing and would NOT start. Jumped and took to dealer. Told Service Manager that I wanted a new battery. First he said it would take a 2 1/2 hour test; told him that would not work for me had to leave on a trip, just put in a battery. He finally agreed, and now everything seems fine.
But believe me I am monitoring this situation. The weird thing is that I had the exact same problem with my NEW 2013 MKZ with 5000 mi. The new battery fixed that problem.. If anyone has had similar, please chime in.