If by, "completely dead" you mean that you had to use the physical key to open the door and the dash was dark, that is your 12V. Everything in the car except the AC, traction motor, and heater operate off the 12V system.
I recently had my 12V issue solved after 5 months. What is happening is something isn't shutting off when you turn the car off. The reason it is so hard to diagnose is there is no logging of what modules do and do not shut off when you turn the car off so they have to catch it in the act of draining the battery in order to fix it. If it's intermittent then that is nearly impossible. Mine was only fixed because it eventually got to the point where it would drain the battery almost every time the car was shut off. In my car the RFA (Remote Function Actuator) and the telematics unit (wireless modem) were drawing excess current when shut off and had to be replaced. I believe the RFA is the module that interacts with the key fobs. I'm not sure what all it does maybe someone more knowledgeable can elaborate.
If you're handy with a multimeter you can do some diagnostics yourself. Shut the car off and unhook one of the 12V battery cables. Then reconnect it thru a multimeter configured to measure current. Before testing mine I used a clamp on DC ammeter to see the current when I shut it off. It was just under 4A and quickly dropped. This clamp on meter is useless below 1A necessitating me putting a multimeter in series with the battery. Most multimeters are rated for 10A so this shouldn't be a problem. However if you turn the car on and the battery is low it can easily jump to near 50A! So DO NOT
turn the car on with the multimeter in series with the battery unless you want to potentially smoke your meter. I know this from experience!
In talking to my dealer I learned the ford procedure is to wait 40 minutes after the car is shut off and the current draw on the battery should be less than 50mA. Mine was 20mA. If the current draw is over 50mA the procedure involves pulling fuses until you find the culprit. The thing that makes this difficult is disconnecting the 12V battery, opening a door, hitting a key fob button, or anything that "wakes the car up" resets the need to wait 40 minutes to see the battery current drain.
I have read of other people having the telematics unit be the culprit. If you don't care about using myford mobile you could pull the F1 fuse in the back to disable the telematics unit and see if that solves the problem. I'm assuming on a 2012 that isn't covered under warranty anymore so it probably wouldn't be worth fixing. Besides I thought they were going to charge for MFM after 5 years anyway. By the way if your manual isn't handy http://www.autogenius.info/ford-focus-e ... a-version/
this page will show you where on the rear fuse block F1 fuse is (bottom 5A fuse toward front of vehicle). Yesterday I pulled this fuse because I noticed my telematics unit stopped responding a week earlier.
Another less likely possibility is your EVSE is faulty.