AudiForums.com - Multiple issues - looking for explanation (who loves a good mystery!)

Hi everyone. I have a 2005 Audi A8L. Around 85K miles. First off, i am not a car guy - so please forgive me if this is basic. Over the past year, I have had 2 issues with this car that have since self corrected. If anyone has any insight, I would appreciate it - if not only for my own sanity, but maybe there is something I should be doing. Here are the issues (I'll try to be brief and stick to the facts):

Issue #1 - At the end of last year (2010), the CD changer stopped working. I forget the exact wording of the error message (something like 'CD Default Error') When I took the car in for the 75K service, asked dealer to take a look. Said it needed to be replaced (cost >$1000). Said not to bother. A few months later, car wouldn't start after sitting a few days in sub-freezing temperatures (engine was having trouble turning over). After trying over the course of a few hours, car finally started. What's better, the CD player all of a sudden was working again with no error message. Strange! But I accepted it - was happy to have that problem fixed.

Issue #2 - About 3-4 months ago, was driving down the street and all of a sudden, my MMI interface went blank. Could not turn it back on and it seemed dead to the world. Looked at these forums and I figured the MMI Interface was dead and by the sounds of it would be a multi-thousand dollar fix. Didn't bother to have it fixed (use the GPS and radio on my android phone - not perfect, but free). Well, yesterday car wouldn't start. Dead battery. Jumped the battery with my wifes minivan, and walla....MMI Interface is working again. Date displayed is March 2004 - seems like it was reset to factory. Strange again.

Two very strange self-correcting issues. Anyway, I'm happy to have all this wonderful technology available to me again, but I am wondering if I need to be doing anything here with this car (e.g., new battery, etc.)

Thanks in advance for any thoughts.