USB/Clock turning on and off overnight
So I recently did an android tablet mod for my 2012 mustang and decided to hook it up to the USB plug instead of the 12v accessory outlet, since USB shuts off with the ignition and the 12v plug stays on 24/7. However I noticed that my tablet was spontaneously turning back on even with the car completely off every minute. It kept going back and forth from "discharging/charging" mode. Every time it did this, I noticed the LED clock would turn on in the head unit of the stereo system. It looks like the car stereo basically power-cycles itself repeatedly all night in some sort of super low power mode (the speakers obviously dont come on). Or perhaps the tablet is somehow invoking the stereo to power cycle even with the ignition off.
I can trickle charge the tablet via the 12v plug, but I'm concerned this could be bad for the battery by drawing power 24/7. As I mentioned, the USB plug seems to turn itself off with the ignition, minus this one little problem I'm having.
Does anyone know precisely how the USB plug is configured in 2011+ GT model cars with the Shaker audio systems? I'm sure many of you probably leave ipods and cellphones in there all night with no issues, but I dont understand what it's doing and why it keeps sending a charge to my tablet on and off throughout the night.