leetski

As you can gleam from the title of the thread, I recently replaced a 6yr old battery with an OEM one because I found out I had to jump start the car way too often after it had been sitting in the garage for <1 week. While this was my first act to mend off "battery drainage symptoms" it would prove that it won't be my last... Namely, the new battery has suffered a similar fate - it keeps draining in between relatively short durations of not starting the car.
Suffice to say, this new found realization provoked me to further investigate what the culprit could be after ruling out the battery (?)... It is at this point, that I turn to you for advice? How would I (no warranty) diagnose why the battery on my 2003 CL55 is draining so frequently? Has anyone experiences similar problems?

I did recently notice my passenger side head rest tilting upwards as if it had a brain of its own. I'm thinking of checking the individual relays? Would anyone have a relay diagram I could reference while tinkering about?

anhnguyen310

Have you checked to see if the alternator is bad or is going bad? I had the same problems but then found out it was my alternator that went out. wasted 88 on a new battery and the problem was still present. Finally just took it in and had the alternator rebuilt for 130, no problems after that

shooter

The old trick is start the car and disconnect the battery. It should run fine, even with a stiff load on it (rear defroster, heated seats, stereo). But if it dies the alternator is going. You can take it to a auto parts store to have it tested. Many places do that.

lightningfast7

That's why it's an "old trick"... you try that on a modern vehicle and you might end up frying the voltage regulator in the alternator.. ESPECIALLY on an electronic vehicle such as a MB. I would seriously suggest you disregard this advice.

izzyz28

Assuming the CLS also has a small battery for the brakes like the W211, replace that battery ASAP. Mine was junk, which was causing it to pull power from the rear battery, destroying it twice.

sunil517

if it is holding load when you turn on lights,seats and fan... if the volt drop with the car running the alt might be on its way out...

with the car off the volt should be 12-13 car running 14 or so ....
Do not disconnect the battery and run the car....

Also if you have a OBDII scan tool some of the unit give you volts reading output also...but its built in to the e63 not sure on E55..

lightningfast7

You can even get the volts in the instrument cluster. I think its key in Pos 1 then the little reset button three times fast.

03'55AMG

^^^ correct, put in in position 1 then press the reset 3 times fast then there should be something like UB:12.x volts (off) and UB:14.x (running)

izzyz28

Correct. However, if it is cold outside don't be surprised if it reads something like 11.7V, especially if you turn the key to position 2. Also, be aware that the voltage displayed is actually .2V less than the actual voltage at the battery. I don't know why, but that's how it reads, especially when the engine isn't running.