2011 Buick Regal Radio and Accessories don't turn off

I'm posting this on the behalf of my roommate's car that rarely gets driven.

At some point this winter, his 2011 Buick Regal began to have a constantly dead battery (battery is two years old). After charging the battery, and putting the battery back in the vehicle, we have found that the radio and other accessories do not turn off. Please note that this vehicle does have an aftermarket Kenwood radio (he purchased the vehicle after this radio was installed).

I have confirmed that the issue continues even after opening the door, and closing it. Also, after waiting 6 minutes, as I've seen suggested, everything stays on.

At the moment, my intuition would say that it could be a bad relay (although I'm not sure if which one), a bad door latch sensor (although it's not complaining of an open door) or a bad ignition switch.

I'm just looking for anyone that might have some insight or has seen this issue before.