Mercedes-Benz C300 auxiliary battery failure warning light after replacing auxiliary battery and voltage regulator on Mercedes-Benz C300

Some Mercedes-Benz C300 owners report experiencing persistent auxiliary battery failure warning lights even after replacing the auxiliary battery and voltage regulator. These owners note that while there may not be a specific warning light for auxiliary battery issues, other dashboard alerts may illuminate if the battery is malfunctioning. Common symptoms reported include dimming lights, irregular start-stop functionality, keyless entry problems, and infotainment system issues. Additionally, some owners find it helpful to use an OBD-II scanner to read diagnostic trouble codes, such as B1D13, which are often associated with auxiliary battery malfunctions. Physical inspections of the battery for damage, corrosion, or loose connections are also recommended, as failures with the voltage converter can trigger error messages indicating an "auxiliary battery malfunction."