This was an accidental finding on my 2013 MCS.

Background: I use an iPod which is tethered to my Android phone. The iPod charges while connected with the Y cable (MiNi Connected with Nav) and I was using a USB receptacle that plugs into the power socket in the center console to keep my Android charged (no requirement for data exchange across the USB interface).

What I discovered is that while the power socket only provides a charge when the engine is running, the USB data port in the glove compartment provides power not only when the engine is off, but when the accessories are also off - as if hard-wired directly to the battery. Great news for those times when I need to maximize the charging time on my phone when running errands.

If that detail was mentioned before, I apologize, but I found nothing of it here on the forum.