Well, I replaced the battery, (new Bosch battery, properly coded), and I'm still having problems with the Nav/radio. It seems to take 2-3 minutes to start up after the car's been sitting for a while. I get the disclaimer message, but clicking the iDrive knob does nothing. Eventually the unit wakes up and performs normally.

Once the unit is up and running, if I shut off the car, and immediately restart the car, the nav/radio comes on immediately.

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2014 BMW 328i Xdrive
2011 BMW 335i M-Sport
2008 BMW X5 4.8i Sport
2000 BMW 528i 5sp