Here's a list of the convenience features that are disabled in two stages (Link).

PM me your email (if you don't have access to the WIS), for a copy of the '03-'06 W211 dual battery system function/component location documents.

If your battery(s) and charging system are in good working order and you still have convenience features disabled or battery messages (dual or single
battery setup), you will need to have a STAR diagnostic check run on the car to figure out what's causing them, as there is no way of telling (besides guessing).

Why be content with error messages or warning lights when you can know for certain what's wrong and fix the problem!