Visit workshop: Red battery message (Mercedes-Benz W211)

The main reasons for BATTERY/ALTERNATOR VISIT WORKSHOP:

‍1. Loose or bad battery terminal connection:

‍You can remove the terminal connections and clean them up just to be sure. Use some sand paper around the terminal post and at the cable end connection to make a clean up.

‍2. Main battery is near the end of its life:

‍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.

‍3. Alternator problem:

‍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.

‍4. Secondary Battery / Auxiliary Battery:

‍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.