C220 CDI W204 2007
1 Found one intermittent draw, namely RH parking lights ON with switch set to OFF. Suggestion: Setting to AUTO fixed it or buy a new light switch for $600!
2 Suggestion is to disconnect the front seats, pulled six plugs underneath but still have the problem.
3 Suggestion from one chap is to put in a 200 Amp relay after the "ignition switch" to cut off the battery completely. Assuming the fault is in the alternator - a new alternator would cost $2,000 with a two/three month wait ex-east or $200 from a wrecker.
4 It is a new Varta battery and voltage at rest is 12.3/12.4. Connected good multimeter (MM) cable firmly to negative pole on battery and MM to cable. Initial draw is in the Amps, but that is OK as the computers boot up.

Watched a fairly permanent draw of 66 - 70 mA, which does not hurt a 100Ah battery, BUT occasionally the amps went up to 200mA, which is too much.
Also, very occasionally the amps dropped to 6mA. The Merc was not locked and the boot was open, which I am supposed to lock with a screwdriver as commentators suggest the car is not sleeping unless it is completely locked.

Questions: Does this 16-year old Merc have "smart charging", where a new battery needs to be "initialled" somehow?

Alternator charges at 14.0V very briefly after starting and drops to 13.7-13.8 during driving. Amp meter tells me with the engine running it charges at 22Amps.

Another commentator suggested a faulty alternator, which is hot after driving, but without taking the steel plate off underneath I cannot check that. One commentator and mechanic remembered a faulty "convenience module" cost a client $4,000 - just after warranty expiry. He did not elaborate what a "convenience module" is.

Thanks for help.