I just installed. New alternator and it stays pretty much at 12.6 idle then sometimes goes up to 13 when accelerating. I have a 2010 e class so not sure if this is normal. The last one was bad and it showed 13.6 and occasionally dropped to 12 ish.
Hey @Dnasty1, in the charging stage it should be between 14.3 and 14.9V. Sometimes when you have new batteries it goes to standby mode when it sits on 12.6V and when you break it goes up. It's almost like with EVs when you break you recuperate the batteries.
Think of it as a backup system. When you disconnect the main battery it holds the memory but not just that. When you use stop/start and the car is off, power comes from the auxiliary. There's so many systems both batteries support. I tried to do some research on exactly what each battery is linked with, but I couldn't find precise answer.
Try to top up the battery and check the menu if the alternator is charging. If yes, your battery is dead. If the light came up while driving it's very likely the alternator is not providing enough charge. Good luck
Mine gave me a red battery with a see operators manual icon. My battery drained while driving and I lost power to pretty much everything. Then it just died
