benz99999, I suspect the voltage regulator brushes are so worn that the alternator is not recharging the battery sufficiently. I am in the process of replacing the voltage regulator in our 1998 E320. You need to remove the alternator, then remove the cover on the back of the alternator to access the voltage regulator. Be sure to disconnect both battery cables before you begin this job.

After you disconnect both electrical leads on the back of the alternator and remove both E14 torx head bolts, use a pry bar to swing the alternator clear of the mounting bracket. To facilitate reassembly move the 2 sleeves in the mounting bracket slightly forward so there is adequate clearance to easily reinstall the alternator in the mounting bracket.

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Fred Hoelzle