I'm writing in trying to identify what exactly is failing. Have had this trouble for a while, where I leave the car for a day or two then it simply won't start. I accessed the UB readings today and found that when everything is off, it reads around 11.5 V. When I turn ignition on, the voltage just keeps on dropping until the screen goes black / cuts out, when I return the key back to position 1, it charges again to 11.5 V. Wondering if anyone who has experienced this or similar knows what's going wrong.

Also, when I have got the car started (by jumpstarting), when I rev, there is a voltage drop initially. However after 20 seconds it seems to stabilise and remains over 14V,even when I rev and all lights on.

Do have electric seats?
If so, sounds like the classic seat module issue.
Bypass with a relay. Search on that one.
Otherwise, as Plutoe says, get a scanner that reads Mercedes codes,
and read the codes to see if anything comes up.

Got a multimeter and found several fuses contributing to a 300+ miliamp draw.



Fuse 8 which I believe is central locking

Fuse 9 which controls the dome lights

Fuses 53, 54, 56 (in the engine bay) which have something to do with the CDI control unit.



Wondering if anyone has any experience with this and what my next steps are.



(I've done load tests and overnight tests with the battery disengaged, battery is perfectly fine)

Also, if anyone could kindly post wiring / circuit diagrams for fuses 8, 53, 54, 56 it would be greatly appreciated! I feel I've made a breakthrough with this problem and I'm wondering if simply replacing the fuses will work or if I'll need to look at the wiring.

Thanks

I take it that's quite bad?

Had the alternator replaced a couple years ago along with the battery, ever since then I've been experiencing the Parasitic Drain.

Wondering what the next steps are,
Thanks

Car runs perfectly fine though when it's jumpstarted - no warning lights about esp/bas, no engine management light etc etc

Did you go to a Euro shop for the alternator replacement? Wondering if the shop fried your front SAM. These cars have to be connected positive first then negative. Doing it the other way cooks the SAM.

You didn't answer the question the other people asked already - does your car have power seats?

The various modules often have a delay after the car is switched off. My SA told me to wait 30 minutes, but personally I found that all modules should be "sleeping" within about 5 minutes of pulling out the key.

The car has no power seats so i guess that's one less potential issue...

The car doesn't exhibit any signs of a blown SAM, atleast what I could find online so I think it's good on that front - everything seems to work fine, no malfunction messages, correct fuel gauge needle etc etc.

I'm thinking of disconnecting the alarm siren tomorrow, have read that that's what contributes to the fuse 8 draw and it could be linked to the SAM too. Could pretty much resolve the draw issue.

Disconnected the alarm siren and the readings (for voltage drop) for fuses 8, 53, 54, 56 have gone to 0. I don't mind leaving fuse 9 disconnected. I think this has solved the issue, will be testing the health of the battery again and will replace if it needs it...

Nice work.