duxthe1 is correct!

Somewhat difficult to diagnosis, the most common issue with that car is the rear SAM staying awake & allowing the interior network to not go asleep.

You could disconnect the power wire to that SAM & see if the battery is still being drained.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator