Low voltage batter drain

The more technology that goes into a car, the more problem areas there are, and one biggie is electrical. You have a parasitic problem. There's a defective switch or control that isn't shutting off, and draws constant current. You need to find it. And from what you've said, you also need to find another mechanic..... I'm assuming you're taking this to the dealer where you bought it, so discuss this with the service manager; he should be able to put someone more qualified on it..... If you're in a state where there's a lemon law, look into this, and if it's not fixed properly the next time, tell them you're initiating a claim over this.

The car should be under warranty. Force FORD to fix this mess