SL/R230: Replaced aux battery now service battery symbol shows
Thread Starter
Junior Member
Joined: May 2016
Posts: 50
Likes: 3
From: Alamagordo NM
2007 sl55
Replaced aux battery now service battery symbol shows
2007 sl55. Is the voltage regulator the black box by the aux battery? Where is voltage regulator? Do i test by checking voltage running/not running? I did not have red alert until i changed aux battery. I checked terminal they are tight. Any advice please
MBWorld Fanatic!
Joined: Mar 2008
Posts: 1,232
Likes: 168
From: Glasgow, Scotland, UK
SL 350 R230 (3.7L with AMG Speedshift autobox)
The voltage regulator is on the back of the alternator, it regulates the 'charging voltage' and sits around 14.1VDC. Testing is easy, connect a multimeter to your cigar lighter or buy a plug in volt meter off amazon and test whilst driving, with the engine ON you should get 14.1 VDC regardless of current consumption i.e try turning your lights on you'll see a 0.1 to 0.3 VDC dip for a sec then revert back to 14.1 VDC as the regulator does its thing. Try adding load on the car such as the rear window heater and heated seats, the regulator should maintain the 14.1 VDC. With the car off check the voltage it should be at least 12.3V anything around 11.5VDC is very low.
The AUX battery is the rear one, not the front that starts the car. If the rear battery is NOT a genuine Mercedes battery they can give issues, when replacing get the genuine Mercedes battery made by Varta, the car will thank you for it, aftermarket batteries just do not have the same longevity. Also check your BCM - Battery Control Module above the battery behind the lining, they can burn out.
The AUX battery is the rear one, not the front that starts the car. If the rear battery is NOT a genuine Mercedes battery they can give issues, when replacing get the genuine Mercedes battery made by Varta, the car will thank you for it, aftermarket batteries just do not have the same longevity. Also check your BCM - Battery Control Module above the battery behind the lining, they can burn out.
Thread Starter
Junior Member
Joined: May 2016
Posts: 50
Likes: 3
From: Alamagordo NM
2007 sl55
Hello thanks. I replaced with battery from dealer. Did not get thank you on dash. Battery sat for a few months before i installed. Curious about battery control module. I started minor messing with it before i got smart enough to get enough slack to get positive terminal off. Everything else in car works. The starter battery was replaced aftermarket less than a year ago. Voltage readout on dash is 14.1v
