2010 Mercedes ml350 blue tec
Well just for background it’s 2010 I’ve never had any problems with it but it started acting like a parasitic drain so I’m getting no codes at all on the code reader but I had the

battery tested and it was original last year and had it replaced with a new one

Have the alternator tested and it’s good

Add the back up battery test, bad and replaced it

Was told that the parasitic drain should be coming from the relay in the fan so I replace the entire fan relay assembly


It would usually take two or three days to drain and now it’s taking literally hours I have a trickle charger on it. I had it charging for almost a week and a half fired up fine drove it to town and it wouldn’t start when I got to town.



When I try to do a parasitic drain test on it, I checked the amperage coming out of the battery by disconnecting the negative ground wire and putting a meter in between I’m getting 20 to 30 mA maximum drain when everything is locked down and quiet in the car I’m told under 50. It’s not an issue.

I have an alpine stereo in the car which reads a voltage and when the car is running I’m getting 13.8 V which again verifies the alternator is working correctly.

Any ideas would be helpful

 

Here is an excellent video that will help you find whatever is draining your battery. Perfect for the W164. Some basic tools and you'll find whatever is draining the battery.

 

Great troubleshooting Dan!