Fast intermittent Battery drain w211

[ady74]

Ive got a very annoying battery drain just happens when it feels like, it was on average every 2weeks but thought Id cured it 3months ago as took the fuse out of the drivers seat module and it worked for 3months untill yesterday.
It will drive fine then you can park it for 15mins and its dead. then wont do it for weeks it will be fine again.
Ive changed both battery's and its been on a star showing nothing.
Question is what are the usual suspects I could try?

 

[mersum1es]

It must be a huge draw of current if it drains battery totally in 15 minutes, nearly 400A!!!! (= not likely). SO I would blame insufficient charge or battery capacity (even stated battery changed, is it tested against load?). What is charge voltage, and battery voltage just after drive?

 

[ady74]

dont know how would I test? a car spares shop that do battery and alternator tests? would that be enough?

 

[Uncle Benz]

Do you have electric memory seat on the passenger side too?

The other thing to consider is the electric engine block heater if you have one. Presume it's diesel?

 

[mersum1es]

W211 diesel electric heater is inside air vent duct and yes it can draw big current when faulty but still it won't exceed 100A (which is already huge amount and heat power).

Seat controls uncle benz mentioned are usual culprit as well as comand system but they cannot drain battery in 15 min, current is there only few Amps.

There are many level battery testers available, I believe any mid priced tester is better that only voltage reading. These digital "Fast" testers are giving directive reading of battery capacity while testers which actually draw batter empty give most accurate result.

 

[Blobcat]

I've had an issue with a regulator pack on an alternator which would drain the battery pretty fast, it depended where the alternator stopped as to if it would drain or not. Refurbed the alternator and all good after that. (That was on a 911)

 

[ady74]

W211 diesel electric heater is inside air vent duct and yes it can draw big current when faulty but still it won't exceed 100A (which is already huge amount and heat power).

Seat controls uncle benz mentioned are usual culprit as well as comand system but they cannot drain battery in 15 min, current is there only few Amps.

There are many level battery testers available, I believe any mid priced tester is better that only voltage reading. These digital "Fast" testers are giving directive reading of battery capacity while testers which actually draw batter empty give most accurate result.

Do you have electric memory seat on the passenger side too?

The other thing to consider is the electric engine block heater if you have one. Presume it's diesel?

Yes electric but not memory seats, yes its a diesel.

 

[ady74]

I've had an issue with a regulator pack on an alternator which would drain the battery pretty fast, it depended where the alternator stopped as to if it would drain or not. Refurbed the alternator and all good after that. (That was on a 911)

Yes my mechanic mentioned this too,im seeing him tomorrow with the car again so wanted to through some idea at him.