Update.

So I tested the battery and alternator yesterday after about a 30 minute drive and 30 minute rest after that. At the battery posts I got about 12.7v - 12.8v at rest, and 13.8v - 14v idle with the headlights and AC on full blast. This was done using a multimeter. I decided to tightened the battery clamps just to be sure nothing gets loosen again in the future while driving. I turned the car on.. and I got the No Crank / No Start issue again. Pulled up INPA, error 209 came back.

FWIW, I have been getting an intermittent message to check break light and back light that seems to be going off and on. Opened my front passenger door to grab things out of that side.

I attempted to reset/resync the rolling codes twice in INPA, didn't get any errors, then did the catch procedure. Still No Crank / No Start. I've also tried an EWS/DME Adaptations reset in PASoft as well.. same result. Is this is a sign of a bad key fob? Or some sort of short in the electrical system?

I'm completely confused as to why this would happen after successfully starting/driving the car multiple times.

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'06 X5 3.0i