[Supervinnie40]

Like I said before, you're not supposed to start the car with this system attached. Nor does it restore the battery in your car to full power.

When the battery goes below a certain point, it won't have enough power to turn over the engine, making starting the car impossible. By connecting this device for a good 10 minutes, it gives the battery in the car just enough juice to start a few times. But you don't try to start on this device. You connect it, wait for 10 or 15 minutes, disconnect it and try to start the car.
If you're unlucky, and the car won't start after a few attempts, the battery in the car will be drained again and your still in trouble.

If something weird happens (like something drained the battery without your realizing it), this can be just enough to get it going again. But nothing more.

I was wondering because there is a system of switches, fuses, ECU's etc. between the battery of the car and the socket. That system was built on the idea that electricity (for example: ) goes from the battery to the ECU, then the BCU, then the fusebox and then the aux socket.
It might not be designed for any electricity 'flowing' in the reverse direction.