Aux Battery Trickle Charger
Thread Starter
Super Member
Joined: Jul 2007
Posts: 742
Likes: 228
From: Santa Barbara, CA
S550C4, Porsche Cayenne
Aux Battery Trickle Charger
During recent routine service, I had the technician connect a MBZ brand charger (previously in my SL) to my auxiliary battery (right side of trunk). But the Fault light will not clear. Does anyone have an idea what the problem may be?
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Joined: Dec 2019
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Thread Starter
Super Member
Joined: Jul 2007
Posts: 742
Likes: 228
From: Santa Barbara, CA
S550C4, Porsche Cayenne
Follow up. I checked the plug that was hard-wired to the battery and got + on the black wire and - on the red wire (not how I learned the electrical conventions back in the day). So took it back and they confirmed my diagnosis, miswired. Fixed and now working OK. Who would have thought that a certified tech would not know Red on Red and Black on Black...
MBWorld God!
Joined: Dec 2019
Posts: 32,222
Likes: 6,279
Follow up. I checked the plug that was hard-wired to the battery and got + on the black wire and - on the red wire (not how I learned the electrical conventions back in the day). So took it back and they confirmed my diagnosis, miswired. Fixed and now working OK. Who would have thought that a certified tech would not know Red on Red and Black on Black...
Newbie
Joined: Feb 2025
Posts: 4
Likes: 1
I have a question unrelated to this particular issue. My S560 cabrio 2019 has an optional plug for a trickle charger (on the left inside the trunk). It works perfectly with the Merc supplied trickle charger. I assume it charges both batteries, starter and auxiliary. Is my assumption correct, otherwise why having this option just for one of the 2 batteries?
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2022 SL 55 AMG, 2020 AMG GT 53, 2015 GL 550
Ridiculous
Follow up. I checked the plug that was hard-wired to the battery and got + on the black wire and - on the red wire (not how I learned the electrical conventions back in the day). So took it back and they confirmed my diagnosis, miswired. Fixed and now working OK. Who would have thought that a certified tech would not know Red on Red and Black on Black...
Just... wow!
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