AZ-IS

I have a 2003 sl55 amg. My battery light comes on and the message, "electrical consumers offline" appears on on my dash. I checked the starting battery in the eng compartment and it tests ok. The rear battery in the trunk failed a load test so I replaced it. While replacing the battery, I checked the alternator and there was 4.3V at the positive post. I replaced the alternator as well. This has changed nothing. I have went through all control modules and checked for related faults only finding 2 faults: b1088 (instrument cluster a1-can communication error) and b1010 (lower control panel module-n72 voltage too low). these faults will not erase and if they do they return immediately.
I have also checked every single fuse in the fuse information page that is located in the trunk and all are ok according to my test light.
Can someone please tell me what I am missing here? Are there any diagrams?

Boston_MB_tuner

Have you tried hooking it up to DAS?