2009 Ford Focus apparant dead battery

Went for a drive (everything OK), stopped and parked up for 5 to 10 minutes with the ignition off. Attempted to shut electric windows before leaving the car to go walking and discovered everything was dead. None of the electrics were working, no warning lights or console information, the ignition would not turn on and the key fob would not lock the car. To all intents and purposes there wasn't a battery in the car. Called for breakdown assistance who gave me a jump start. Ran the car for half and hour and it has continued to perform perfectly since having been run several times. My local garage couldn't find any fault with it.
I have noticed since however that although I can correctly set the time, day and month on the console it will not let me select a year after 2014. Strange!