Help - 2004 Mercedes SL55 AMG - VISIT WORKSHOP, RED BATTERY LIGHT, ABC, ROOF OPEN ALERTS. NO CODES

[@SLAMG1]

It’s your alternator man

[@jvakos]

yes the voltage regulator was definitely bad... i replaced it a week ago and finally the new battery is charging properly. was original voltage regulator at 75k miles and brushes worn down

[@jvakos]

Quick update - seems my auxiliary battery in the trunk was very low voltage and is causing my issue. I hooked it up to my Noco Genius 3500 trickle charger and it was showing at 25%. After charging the battery for 24 hours it’s now showing 100% and I will take it for a drive and see if that was the issue.

[@elijahlane411]

Have you found the issue?

[@jvakos]

@@elijahlane411 looks like the issue was a weak auxiliary battery in the trunk that couldnt properly supply power to all the accessories. I've kept the rear battery on a trickle charger during evenings and not had the issue come up again fortunately.

[@jvakos]

@@elijahlane411 yes it was my Voltage regulator actually. I replaced that myself as you can get to it from underneath the car and dont need a lift. its a bit tricky to remove from the alternator but very doable if you are patient.... NO issues now with battery charging. voltage regulator was at 75k miles and seems about the time when those brushes wear down.