: Use a multimeter; a healthy battery should read around 12.6V . If it is below 12V, it likely needs replacement.
: Look for a non-functional ECO start-stop, disabled "Hold" brake function, or erratic infotainment behavior. How Do I Fix My Mercedes Auxiliary Battery Malfunction?
: Use an OBD-II scanner to look for battery-specific codes like B15DC00 or B142E . Common Locations by Model : Use a multimeter; a healthy battery should read around 12