red battery light indicator comes on in the instrument display signalling an issue with the charging system of the car i guess.
when i turn the car off and back on,it disappears for a while...sometimes and hour, sometimes 2 hours or more. but lately been doing it within an hour to two of shutting and restarting the car. In all cases, car drives absolutely fine and normal.no loss of power anywhere whatsoever.
Anyone experience this? Am guessing its either the alternator or one of the batteries. Just want to see if anyone has had a similar issue.


Thanks

 

Just the small starter battery. Just replaced mine wit a similar issue

 

Just an update in case anyone faces a similar issue,it was the alternator that was faulty. Alternator changed and everything back to smooth running.

 

How much?

 

everything cost $600. But this was done through my personal mechanic and covered by my extended third party warranty.

 

I recently had an intermittent red battery warning light popping up in my instrument cluster of my 2007 MB S550 (W221). I feared that it could be Alternator or the Control Module. This battery warning light icon comes in two colors Orange and Red. Orange means that battery is temporarily low on voltage and Red icon means that battery is not charging.


I took my S550 to a MB dealership to test and confirm the cause. They tested the front auxilary starter battery (smaller battery in the passenger side front hood) and it tested fine while running and under load. They then tested the trunk battery (big main 180Amp battery) and it showed 14V while the vehicle was running and very low voltage under load and when engine not running. The big battery in the trunk was the culprit.


In short if you see only the red battery icon with no verbiage then it's one of the failing batteries needing replacement. If your vehicle has problem with the Alternator, Voltage Regulator or the Control Module then the red battery icon will accompany text "Visit the Workshop".


This was what I found from my experience. The front small battery sells for $89 and the large trunk battery for $190 at the Autozone and works equally well with three years warranty.

 

Is this the first time you've replaced the battery in the trunk?
Mine is 08 with 31000 miles and I had to replace the starter battery last year.
Consumer battery in the trunk is still good, but I'm wondering how long it's supposed to last, it's been ten years. Then again, I had Porsche Cayenne and its original battery lasted 9 years and 110,000 miles before replacement.

 

Actually the consumer battery in the trunk does most of the heavy lifting and is critical. I replaced this battery for the first time in 9 years and this was the original Bosch Varta battery. If your vehicle is 8-9 years old and you have not changed then it is pretty much approaching the end of its life cycle. This battery at this stage will sneak up on you intermittently and then very quickly die out at this age. A lot of mechanics will try to take advantage of your urgency by tricking you in to buying an $850 rebuilt Alternator but that is totally unnecessary.

This is a pretty cool DIY project and for your 2008 MBZ although you have low mileage, but I will recommend you to replace this consumer battery so it does not die on you when you need it most. MB dealership sells the original Bosch Varta for $240+tax with a core refund of $18. Be aware that this battery weighs 75lbs. My advise buy Duralast from Autozone for $190 with $18 core refund and then install it yourself as a mechanic will not do this as nicely and carefully as you will. To DIY it, you will need to pry out the cardboard firewall in your trunk behind the rear seat from within the trunk. This battery is located on the right passenger side under circuit boards and lots of connections. All you need to do is to open one (1) screw in the bottom and the belt harness will come out, carefully disconnect -ve terminal first and then the +ve one. Gently move the battery left and right several times to slide it out from a cramped slot and put the replacement battery in. You will have to sit inside the trunk to do this job. Total time from start to end to do this battery replacement is approximately 30 minutes.

Also don't forget to put anti-corrosive gel and red/black round pads around the two electrodes of the new battery. Seat round pads first and then apply small quantity of gel around and on top of both the electrodes. As a word of caution after the new consumer battery is installed and it kicks in a lot of stuff in your car like windows and several instruments will not function normally for at least an hour. You will hear a lot of faint click and clock sounds from all around your car. The reason is the main vehicle control computer located in the left side wall of the trunk will reboot and will perform self test, diagnostics and auto-calibration procedures. Once the computer is fully rebooted, it will re-calibrate every sensor and actuator in the car and that will take some time. No need to be alarmed. Try to manually power up and down the windows and they will start functioning normally within few minutes. Preferably after one hour after installing new battery, drive your car for about 30 miles to fully charge the new battery and for the rebooted computer to generate and build vehicle related data. Love this self-calibrating German engineering!

 

amriyaz, thank you for your comments.

 

my 2011 s 550 battery sign came up I replaced the main battery the sign didn't go away , I replace the altinator the sign still shows what do I do next anyone with the same issue please help

 

First thing you should do is to change the other battery. S550 has two batteries one under the hood and the other in the trunk. Hopefully this should fix this. If you still get a red battery sign then it means that the control module that manages both the batteries needs replacement. That is an expensive part to replace so hopefully second battery change may do the job.

 

Btw be very careful about the red battery sign on your dashboard as it means that the batteries in your car are not being charged and pretty soon they will be discharged and may get permanently damaged. The S550 is an advanced vehicle and almost all its critical systems are electrically driven. The transmission on this vehicle is also electrical and low voltage and current can also potentially damage it. My recommendation is to treat this matter as urgent before this situation causes unnecessary damage to your vehicle.

 

I believe that 2011 has just one battery under the hood, and no battery in the trunk.

 

"I believe that 2011 has just one battery under the hood, and no battery in the trunk."

You are correct.

 

2008 E320 diesel, I changed battery and alternator still intermittent battery light, no message though

 

My issue turned out to be a bad ECM not sending a signal to the voltage regulator on the back of the alternator. That in turn led to the battery not being charged.

 

Thanks Mercmuscle, but my battery seems to be charging

 

Hey guys, I have a w221. My red battery light was on for a while, 2 months, couple days ago red light, abs esp off all lights were on and the system on the nav screen did a counter and shut down. Got the car towed. Checked your forums, replaced the trunk battery. Got the car today, red battery light back on yikes! Voltage of alternator is fine and so is the dashboard battery good. Could it be the voltage regulator? If so, is there one in the trunk and one in the front? Pls help. New here

 

Hey man, I will help you where I can. My car was at the dealer for nearly 9 months for the same issue because I’m currently stationed in Germany and my car is US spec. Don’t believe what they tell you about parts being cheaper here or service being easy or buying the cars here as being cheaper because they don’t even sell the S550 here. Every time I go to a dealer you would think I had a damn Maybach!!

My car is a 2011 facelift model so I don’t have the trunk battery. In my case I had put a new battery in the car, installed 4 different Bosch alternators (I thought they had been sending me the wrong parts lol) and had replaced the voltage regulator on my stock alternator that came with the car. So to answer one of your questions, your alternator should definitely have a voltage regulator installed on the back of it. Also, the dealer told me that my alternator needed to be replaced but what they didn’t know is that I had installed the stock alternator back on the car with the new voltage regulator and everything is still working fine to this day. I also had voltage at the alternator but after many months at the dealer they found that my ECM, (that little gray box installed on top of your motor) was not sending a signal to the voltage regulator to charge the battery. After €4000 and 9 months of programming I finally got my car back.

 

Hi after having the same problem with my s350 for months found the solution, my son being a instrument tech found a flaw indesign, when you lift or remove the cradle that holds the battery at the front you will see the loom going through the fire wall, this causes a short or brake to the rear battery as it needs to make a 90 degree turn we soldered a new wire in and no more problems you might need to peel back a piece of cover to see broken wire.

 

No , the largest battery in the car is the starter battery.

The small auxiliary battery exists to provide voltage for shifting the transmission out of park should the main battery fail. The little lever on the steering column activates an electronic solenoid.

The location of the auxiliary battery was changed to within the dash on later models with main battery under hood.

 

HELP I CURRENTLY HAVE THIS PROBLEM I HAVE A NEW BATTERY AND A NEW ALTERNATOR.

 

Please do not be fooled by this warning light. This is a serious issue. The fixes are many and range from $100 to $7500. The alternator is the first thing to have checked. Advance Auto, Auto Zone, Reilly’s can all check this FIRST or the dealer. I never suggest a MB dealer to start with. Buy an OBD reader if you can. When this battery shows up, it’s giving you a warning that something in the charging system is NOT working properly.
In the S550, the trunk battery literally runs every computer in the car. This INCLUDES the transmission, ABS/EBS, parking brake, power steering, ALL sensors. If this battery drops below 12 AMP output, all computer driven systems start shutting down. I ended up on the side of I-70 with NOTHING working in my car. Nav system, 4-way emergency flashers, radio, brakes, ALL stopped working within 5 minutes of that light showing up on my dash. With a loud “THUD”, the transmission disengaged. It also dropped all the air out of the suspension. This light is NO JOKE. So here’s the short version...Alternator $475, New Trunk Battery $225, Jasper Rebuilt Transmission $2895, ABS sensors $175, ECM $675, and LABOR $4979...tax $565 = $9989. This power loss in your MB isn’t cheap. It’s expensive!!! Simply changing the battery in the trunk is not the answer. Find out WHY the battery discharged to start with. A voltage regulator is a common issue on the 550 motor. It’s an inexpensive fix and takes 5 minutes to replace. The alternator is a $475 issue and takes about 2 hours from underneath the car. DO NOT use the method of removing the alternator from the top. You nearly have to remove everything between the alternator and the radiator!!! If you can afford OEM parts, use them. Aftermarket work too but verify warranties first. Jasper gives a 1 year unlimited mileage warranty on their transmissions. Dealerships often tell you they’ve fixed an issue only for you to return in 2 weeks with the same issue. Try an independent garage first. Their labor rates are often $20-$50 an hour CHEAPER than a dealership and they will use your parts.

 

Hello!

Mbw newbie here. I have a similar issue. Started getting the red battery sign after which a bunch of errors would pop up and followed by loss of power steering. I checked the battery - it was dead so got it replaced and the car worked fine for a few hours (all the error messages disappeared) before it started acting up again on repeat. Took the car to a mechanic where he very confidently claimed it was the alternator that wasn't charging the battery so I got that replaced as well but voila! New battery, new alternator - still have the same issue. The mechanic just straight up said that the ECU was burnt but I doubt it - I got a second consult and read that it's very rare for the ECU to be damaged because of the battery. I've read a ton about the front SAM being at fault, CANBUS connectors, alternators, etc. but I'm currently directionless. Anyone make any progress on this thread or have any suggestions for me?

 

i m having the same issue. Using the “secret menu” to follow the voltage, I nailed it down to a correlation with the radiator fan being on.
Try to see when and what is impacting your voltage.
Also see my post to follow what happens to my case. It might help.