The car is not driven very often, as it is my sons car who is in the process of getting his license.

Battery does not seem to hold charge. Had to jump the car last Saturday, starts every time when being jumped. Drove it for 30 miles, stopped a couple times and restarted without any issue.
Parked the car and tried to start it this morning, and it appears that the battery once again is not strong enough to start the car.
So within 5 days, the battery is dead.

- Is it an older, weak battery that just no longer holds charge and should be replaced? It is the same battery since I purchased it, have not checked for a manufacturing date yet.

- Is there something which is draining the battery when the car is parked?

Thanks in advance.

 

Does the car have full power seats with the memory control on the door? In pre-facelift W203’s that is a common source of battery drain.

 

Thank you Kevin.

YES, the car does have the power seats as well as memory feature.

So, what to do when the car is parked for a few days? Pull a fuse to eliminate the power draw?

Thanks again.

 

Although that is a common problem, there may be other causes. I recommend that you search on topics such a "battery drain." You should find some suggestions for troubleshooting and confirming the cause of the problem.

Your original idea - an aging battery could also be the problem. If you have a multimeter you can check the battery voltage at the battery fairly easily. On the facelift models, you can bring up the voltage reading on the center screen. I'm not sure how to do that on a pre-facelift model. If you can do it, that might show a charging issue.

Good luck.

 

^ Basically modify the wiring so that the power seat modules are driven by switched power instead of constant power. There's also an updated seat module PN where the issue is fixed. At least I think I read that somewhere. However it's much cheaper to just modify the wiring.

To check the battery voltage on a pre-facelift car, turn the key to position 1 then push the trip reset (button next to the tachometer) button 3 times. You'll hear a beep and an extra menu will appear. Turn the key to position 2 and you'll be able to cycle through the new menu. This menu also lets you check the exact engine oil level, as well as turn on dyno mode.

 

Thanks very much Kevin, much appreciated.
I watched this YouTube video, the fix seems very simple and definitely does make sense.

Has anyone tried it here, will it fix the issue?

I have also checked the age of the battery, stamped 02/2017. This means the battery is almost 5 years old, so I am thinking this as well could be an issue? Especially in the hot Northern CA climate. Car is black, so I am thinking it will take a beating while parked during the day.
Should the battery last longer than 5 years?

 

Thanks very much to you as well slammer!

I was able to get another/different menu after pushing the trip reset button 3 times. Thanks again.

 

You may also be able to install the updated seat control modules from a post facelift car. The part number that fits under the driver’s seat is A 211 870 49 26. The passenger side is A211 870 50 26. I think people initially decided against replacing the seat modules because they had to buy new modules and they were expensive. When I Retrofit seat memory in my car I was able to find the driver’s-side module in a pick and pull yard. I had to buy the passenger-side on eBay. Mercedes used the same module in several models and they are readily available for around $50.

 

Thanks. I am perfectly fine with the cheap fix of cutting the wire. I mean, how often do you adjust the seat in your car, and then only with no key inserted and no power? This will be my sons car, so he will most likely never move the seat, possibly while cleaning the inside. Then one just puts the key in the ignition, not a big deal.


What about the age of the battery?

 

I installed seats from a 2009 C63 in my car. The seats have deep side bolsters and I need to move them back when I enter and exit the car or I will rub against the leather and damage it. I recently figured out how to activate the EZ out feature and that takes care of the adjustment automatically. Admittedly, this is a special case and for most people, cutting the wiring may be all they need to do.

The battery could be the problem and you should definitely have that checked.

 

Thanks Kevin.

 

Unplugged the seat modules, and no more battery draining issues.

I will perform the fix as described in the YouTube video over the Holidays.

Thanks for the help, ........ as always.

 

So, after taking care of the seat modules, all was good for quite some time. The car still does not get driven daily, so after it sitting for a week or so, I had to jump it to be able to start it.​​​​​​​​​​​​​​Today, I checked the display prior to jumping it and the battery voltage was at 8.6, obviously not enough to start the car. ​​​​​​​Tried to jump it and nothing happened, no crank, absolutely nothing. ​​​​​​​ ​​​​​​​Got 2 messages on the display:​​​​​​​ ​​​​​​​- Restraint System Service SRS​​​​​​​​​​​​​​- Teleaid Drive to Workshop! SOS​​​​​​​ ​​​​​​​ ​​​​​​​Can an old battery no longer holding charge cause the issue? I was of the impression that one should always be able to jump a car, even with a bad battery? ​​​​​​​What could be the issue? ​​​​​​​Thanks in advance.​​​​​​​ ​​​​​​​ ​​​​​​​​​​​​​​

 

​​​​​​​Anyone?

 

Just to confirm, you did the fix for both front seats?

Also how new is the battery?

 

Yes, I did do the fix on the front seats and all is working properly. Battery is 5 years old, according to the date stamp on it.

 

The hot weather might've done you in. But before you replace the battery, try jumping the car again. I would try letting the other car run for at least a minute with the cables connected so that the battery has time to juice up a bit. Below 11V or so the car will refuse to crank. Some sort of safety feature.

I would also check the quiescent power draw on the battery. Turn off the car and disconnect the negative cable, then install an ammeter in series, and watch over a few hours. According to my SA it can take up to 30-45 minutes for the car to reach this level of "sleep" mode, though anecdotally I remember it was more like 5 minutes. Actually pretty cool to watch the current draw drop in stages as the various modules shut off. The quiescent draw should be under 50mA total assuming the electrical system has not been modified.

At my latitude the battery lasts about 8 or so years. Considering your area is much warmer, 5 years sounds about right.

 

Many thanks slammer. ​​​​​​​So it sounds like all is pointing to a bad battery I guess.

 

The battery was indeed the culprit. Installed a new BOSCH battery and all is working fine again.