Originally Posted by jphughan
The glovebox port doesn't stay powered when the car is off. As for the console port, it definitely stayed powered for a few minutes after I turned the car off and locked the door, judging by the charging indicator on my mobile hotspot. It might turn off after a longer period of time, but it remained active longer than I was willing to sit there and watch -- and like you I didn't want to just leave it there long-term and potentially drain my battery (or find it had shut off and then not know how long the cutoff is).
I suspect that even if it was constant on, it would be more of an issue leaving your car sitting without an alternator charging the battery now and then. The electrical draw from a USB port would take a LONG time to discharge a 12V car battery. I'd suspect that the draw would be not much greater than the battery's self-discharge rate.