For wider exposure for your issues, Benzworld has an active W210 group. MBWorld also a possibility.

I have the same car - 1998 E320. Low battery voltage at user or poor connections could cause those sort of problems. Could also be you have a short or drain somewhere.

When I had similar but not as severe problems, I changed the battery even although it was fairly new. Solved problem and I later used the old battery in another car that was not so sensitive to battery voltage! Maybe get battery and alternator tested at a shop or if maybe a parts store. Current leak can be in alternator.

I also recall measuring battery drain current while removing fuses. That may pinpoint your problem if it is not the battery that is defective.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5