Mercedes G Klasse Battery Issue

Your symptoms point to an electrical system issue, and a defective car battery sensor is a plausible explanation. The sensor monitors the battery’s state of charge, relaying this information to the car's computer. If faulty, it can cause incorrect charging cycles, resulting in a discharged battery. Have you noticed any unusual electrical drain, like lights staying on after the car is off, or aftermarket accessories drawing excessive power when idle? Before replacing the sensor, test the battery's voltage and charging rate with a multimeter. A healthy battery should read around 12.6 volts when the engine is off and about 13.7 to 14.7 volts when the engine is running. This will help determine if the car battery itself is working correctly.

Thank you for the detailed response. I don't think there are any obvious sources of electrical drain, and I haven't installed any aftermarket accessories. Could you elaborate on the specific steps for the multimeter test and where to connect the probes? I'm not experienced with electrical testing.

To test the battery with a multimeter, set it to DC voltage mode, usually 'VDC' or 'DCV'. Connect the red probe to the positive battery terminal, marked '+', and the black probe to the negative terminal, marked '-'. Make sure the probes make good contact. With the engine off, note the voltage. A fully charged battery should read about 12.6 volts. Next, start the engine and repeat the measurement. The voltage should now be between 13.7 and 14.7 volts, indicating the alternator is charging the battery. If the readings are off, it could mean a faulty battery, alternator, or a defective sensor. Given your observations and the potential complexity, it may be best to consult a qualified technician for a thorough inspection. Ignoring the low battery warnings could cause further damage, so professional diagnosis is recommended.

I appreciate your assistance and clear instructions. I brought the car to a certified Mercedes-Benz workshop. The diagnosis confirmed the battery sensor was defective. The repair, including the sensor replacement and labor, cost 315€. Since the repair, the error message is gone, the lights no longer flicker, and the car starts reliably. Thank you again for your guidance.