Well, I got the dreaded red battery light "visit workshop" message coming on intermittently. I actually changed my voltage regulator as this is usually the fix, but the message stays.

I put the car on my DAS and actually got a fault on my battery control module. The car runs and drives fine, but my voltage is at 12.6-13.1. No issue starting it and hasn't died on me yet. Before I bite the bullet and order a new control module ($360 plus shipping), is there any other related thing I could and should check that would cause a fault to the system?

 

do you have an aftermarket audio system? does it come on when the bass is up or pounding?? if you dont have anything that is triggering it and its just seem random, then before buying the bcm, how old is the small battery up front? get that battery checked first and then move on to the trunk battery: how old is that battery? when you checked the voltage, was the car running? check these batteries with the car off and see what your voltages are: voltages on both batteries should be greater than 12.6 volts with the car off.

 

No aftermarket system.
The primary battery isn't old at all. Just under a year. The startup battery is a different story. I have no idea how old that one is.

I rechecked my voltage while driving and now it's holding steady at 13.8 while driving, which is normal. The voltage is not fluctuating wildly in either direction even when parked. However, the fault is indeed active.

I'll let it sit overnight and check again tomorrow.

 

BCM controllers decides when/how long to charge either battery in the AMG. I would top them both off, usually it gives errors if it detects that the batterys are not holding charge.

 

13.8V is not normal, 14.1 - 14.2Volts is normal. Old batteries become huge resistors and start to effect all electronics eventually.

 

agree with above posts. the good news: the 13.8 volts that you do see is a sign that your alternator is working its butt off trying to charge and keep it all up to par. tomorrow before start up, check that front battery voltage while car is off. i would expect that maybe the cause of some of your problems.

 

When did you change the voltage regulator?

 

The front battery is for your brakes, shouldn't neglect it.

 

Yesterday before I posted this thread.

 

Well, the front battery was definitely the issue. Apparently it hadn't been changed since the car was new as it had a date of 04 on it. That, and the front post was so acid corroded that the positive lead was hanging by a thread.

Thanks for the help. I actually half forgot about that battery altogether.