And then this happened....
On the way to work the Pioneer satellite receiver stopped working once again, while at the same time the tire pressure monitor system threw up a flag. They were unrelated, as a front tire was low, but it reminded me that the dealership deflated the tires to 34 PSI from 38 PSI at the last service, which may be why my I5 adventure was more enjoyable.
The steering, traction control and TPMS lights lit up, making me wonder if the car was even safe to move, or whether I somehow shorted out the entire system with my battery trick.
The owner's manual thankfully reported this behavior as normal, recommending a short drive to reset everything. That did the trick, but I admit I was a bit concerned.