Home > Troubleshooting > Electrical Problems > BATTERY/ALTERNATOR VISIT WORKSHOP DIY



Typically you get BATTERY/ALTERNATOR VISIT WORKSHOP warning when the electrical system voltage in the car is below 12.6 volt. When the car is running the alternator produces electricity and the voltage should be above 13.5 volt. If you have a multimeter like this one, you can connect it to the battery terminals to get a voltage reading.


  1. Main battery is near the end of it’s life.
  2. Alternator problem
  3. Secondary (Aux) Battery needs replacing (if applicable). 
  4. Loose or bad battery terminal connection.

battery malfunction

Just because you are able to start the car in the morning doesn’t mean that your main battery is in good condition. The battery may be near the end of it’s life and it doesn’t provide the necessary. If you have a voltmeter you can check the main battery before starting the car. It should have about 12.5 volts. If it is lower than 12, you need a new battery.
Here is a simple test you can perform if you get Battery Defective message at start up. Let the car run for about 10 -15 minutes. Then go turn off the car, make sure all the light are off and nothing is on for a 30 seconds or so. Then start your car back up again. Do you still get the Battery Defective message again? If you don’t than your main battery is not holding a charge properly especially if the car was sitting for a long time. You will be ok to drive the car, but replace the battery as soon as you can before it is not going to last very long.  Mercedes uses battery group 49 and you want to save some $$$ you can get a AGM battery which is what the dealer uses for less on Amazon. Here is a highly rated battery on Amazon that will fit Mercedes Benz cars.
More often than not, the real problem is the voltage regulator in the alternator. You can replace just the voltage regulator if you know that is the real problem. Otherwise you need to replace the whole alternator. Before you replace the alternator make sure that your battery is not the problem. One thing you can do to troubleshoot your car is to go to Advance Auto Parts or AutoZone and have them do a FREE alternator / battery check. This test may be able to point you in the right direction.
Some Mercedes Benz models such as the E Class or the CLS Class have a secondary battery. This is a smaller 12 volt auxiliary battery that is used as back up. The system also checks the voltage of this battery and if it is lower than 12.6 volts you will get the error on your dashboard. So if you replaced the main battery and were wondering why you are getting the Battery/Alternator Visit Workshop message then check this battery as well. Before you start the car after it was sitting for a few hours or overnight, grab a multimeter and check the voltage at the secondary and the main battery. If you have less than 12.5 volts at either one, you know your problem. You can get a multimeter for testing on Amazon for about $20, and they are very easy to use even if you never have used one before. For example  this one, 
4. Battery Terminals
This may sound like to obvious but it was driving me crazy one time on an E Class. I was getting the Battery Visit Workshop message and I knew I had good batteries. It turned out the battery terminal for the negative post was loose and was causing this problem. You can remove the terminal connections and clean them up just to be sure. I use some sand paper around the terminal post and at the cable end connection to make a clean up.
These are the main reasons why you are getting the Battery Alternator Visit Workshop Error Message. If you need to replace any of the batteries you can order them on Amazon using the links below and also help us at the same time.
Malfunction electrical consumers switched off.
You may get Electronic Consumers switched off when the car’s computer has detected a low voltage. This happens when the main battery is old and is going bad. Test the main battery and replace if defective.

Before you start troubleshooting you need to know if you car has one or two batteries. Why some models have two batteries?

According to Mercedes Benz the main battery, usually found in the trunk, supplies the on-board electrical system in normal operation. While the secondary (auxulary battery is a short-time backup for the power supply in the event of the on-board system battery failing. E Class W211, CLS Class for example have two batteries. 

Sequence of electrical system:


• The battery control module monitors the operating states as well as the voltage conditions in the vehicle.
• Depending on the performance measured for the battery, consumers can be switched off in 2 priorities (switched off by means of CAN message). In this case you may get error message saying: 
malfunction electrical consumers switched off. Check your batteries and alternator. 
• The battery control module (BCM) also activates the battery isolating relay (K57/2) if necessary. A distinction is made between 2 states:
– recharging of additional battery
– engaging additional battery in critical on-board network situations

N82 Battery control module (BCM)

The battery control module is installed in the trunk to monitor the batteries (the installation position depends on the equipment. Minispare/full-spare wheel or Tirefit).

The tasks of the battery control module are:
• Detecting the battery state
• Switching off consumers (energy management)
• Connecting the additional battery if necessary (through the battery isolating relay K57/2)

If you have any questions or comments please feel free to post below in the comments section. 


  1. Hello, I’ve got a tricky “Visit workshop!” issue on a 2003 E55, and hopefully you can offer some hints to track it down.

    When I start the car cold, its completely fine. 75-100% of the time when I start the car warm/hot I get the “Visit workshop!” error with the battery icon. I replaced the BCM and the front pre-fuse box in the passenger footwell, but neither helped.

    The alternator is putting out good voltage, and a digital battery charger with an on-board alternator test said its Good.

    DAS shows error 9055 in the BCM and ECU: “The terminal 61 signal on the CAN bus is missing or is faulty.” The ECU has a guided test for this, and shows terminal 61 is OK. I looked up the diagrams and it appears that this is a 2-wire connector from the Driver-side SAM to the voltage regulator. The harness and wire seems fine on both ends.

    At this point I’m not sure where to go next. Considering replacing the alternator, replacing the SAM, or running new wires for terminal 61.

    I’ve seen references to component F56 “Starter, alternator fuse (in wiring harness)” and that it could be the problem, but I can’t find this component. I even purchased a used cable and took it apart, nothing there but thick wire. Also, this wire seems impossible to replace without pulling the motor since its on a bracket which is attached to a bellhousing bolt and there is no space to get a torqy tool in there.

    Thank you!
    Mike K.

    • That is definitely tricky and not normal. As I read you post can’t help but think that this may be a loose contact in the charging circuit or a bad ground. The terminal 61 may be the issue as well. It may test fine when you are doing the test but that doesn’t mean that it can’t be a loose contact and acts up at random.

  2. something is draining my main trunk battery on my 2005 E320 v6 gas sedan
    I removed all fuses front and back to pinpoint and I still had the drain…
    I do not have any warning lights or messages,
    now I am considering installing a battery cut off to keep the battery charged
    so I can start the car when I want with no problems.
    Is there a negative effect to this solution?

    • You will loose the sync function of seats, windows, sunroof and radio every time you cut power like that. Other than that it shouldn’t effect anything when you do this a few times. That doesn’t mean that doing this over and over again couldn’t result in unpredicted effects.

      Check for a current draw one more time. You may get lucky this time. It has to be one of the circuit protected by one of the fuses.

  3. I have a e350 mercedes benz the battery/alternator light was on..I had the battery checked; it was weak..I got a new battery..the light still comes on but it doesn’t stay on..comes on and go off in spurts….i have one battery in the trunk…

  4. My 2003 mercedes e w211 diesel is showing battery visit workshop . Even i changed the battery . The problem is when we start the car it will be fine showing the malfunction after running of 20 mins it gets suddenly switch off showing ignition light’s

    • This can be tricky to diagnose. It may be something as easy a bad ground. You will need to connect your car to a diagnostic scanner to get a better idea what is causing the error message.

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