Auxiliary battery malfunction on SL

Oh man, that sounds frustrating. I had a similar issue with my SL. A voltage drop during engine start was my first clue, followed by all sorts of weird electrical issues. For me it was a classic battery failure. I'd check the connections to make sure they are clean and tight, but it sounds like the aux battery is done. It messes with the whole power management system when it goes bad.

Thanks for the reply. When you say 'similar issue,' was it exactly the same symptoms? Did it happen suddenly?

Yeah, pretty much the same. The error message popped up suddenly one morning, engine start was rough, and the electrical stuff got progressively worse over a couple of days. I messed around trying to charge it, but in the end, a battery replacement was the only fix. If you're not comfortable doing it yourself, I'd suggest taking it to a workshop. It cost me around 290€ to get it sorted.

Thanks. Your experience confirms my suspicion. I'll get the battery replaced. I appreciate your help.