Sorry, no help, other than moral support - the exact same thing happened to me today, and sent me off to search the internet for solutions.
No wifi connection to defrost the car. Eventually I went out got in, and put the car on with the charger still on, and turned on front defrost and rear plus heated seats and stearing wheel. Plus front and rear wipers. Then nipped back inside for a while.
Came back out and car dead except wipers still going - and couldn't be turned off !
From you-tube I learned where the rear release is, climbed in, and then learned that you need to open the bonnet to check the battery !
3V so I felt a lot better that this was at least not some 'back to the service centre on a flatbed' type problem
Jump leads allowed the beast to wake up, and it seems OK except it had a 'charging system fault' code when I turned it back off again. For what its worth I've put it on to charge like an old fashioned ICE car (thought I'd left that sort of thing behind!)
Question to the forum:
From what I understand the 12V battery should be charged whilst its plugged in, so is it fair to assume that if it has gone flat anyway that it will need replacing ?