Start your car in Test Mode by holding the left 'OK' button for a few seconds and then while still holding the button start the car and continue to hold for another few seconds. Once test mode displays on the screen between the guages, use the up or down arrow to navigate to the battery volts screen. If its below 12 that's an issue with a bad battery or faulty alternator. I think mine is actually always around 13 volts which seems a little high actually.
Good luck. If it happens again take a pic and bring it to the dealer.
2012 Oxford White Focus Hatchback
Dyno #'s 164.35 HP 147.12 TQ