I moved this from normal tech help section:

Hi Guys
Car is a 2004 S320CDi (in the UK). We have been through 3 batteries in 12 months. Car is used regularly. Local official MB tech at dealer can find nothing wrong. Alternator has been checked. Last time the tech came out he put a meter on the battery while car was off and said it was normal.
I have read posts about COMMAND or navi unit not powering down, or faulty seat module.
Does anyone have any ideas how to diagnose correctly? This is for my Dad (I am in Canada). I would like to call an independent auto electrician and give him/her some ideas of what to look for.
Thanks in advance
Ollie

__________________
Oliver

Please post your VIN#.


.

__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

Hi

Thanks for looking into it. VIN# is WDB2200252A417054.

When the battery drains, it is completely flat too. Can't even open the doors with keyless go, or with the fob.

Thank you again

Oliver

__________________
Oliver

Do you know if it is a difficult job to unhook the battery? I thought my Dad could keep a spare in his garage and swap it himself when it happens again.

Thanks

Ollie

__________________
Oliver

My Dad is going to take it back to the dealer. I have had a read online and we are going to ask them to troubleshoot the seat modules and OCP. I remember in the past the OCP making a very faint humming/buzzing noise when the engine was off.
Ollie

__________________
Oliver