I hope its not the battery, its around 2 years old, maybe 2 1/2 it should have plenty of life left or there is an electrical problem somewhere although the car seems fine otherwise.
On another note I got alldatadiy.com to work. However so far I cannot find the diagrams that show how to get to and replace the vacuum elements.

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1996 E320
2000 C230 Kompressor
1988 190e 2.3 - 225K miles, owned for 7 years. I cannot say enough good things about this car. Very well built, even at 225 it ran like new.