Mercedes CLA Hybrid Alarm System Defect

That's a bit of a bummer. I had a similar issue with my Mercedes CLA, though it's not a hybrid. I had car alarm problems and saw some weird error messages pop up. Have you had a battery check done recently? For me it was indeed the auxiliary battery giving up the ghost. Is it possible the car alarm system is draining the battery somehow? It might be worth looking into before you replace the battery, just in case.

When you experienced this issue with your CLA, did the error message specifically mention the 'additional battery' or 'auxiliary battery'? Also, were there any other noticeable symptoms beyond the alarm system malfunction? I appreciate the suggestion to investigate potential drain sources; do you have any recommendations on how to effectively conduct such a check?

Okay, so I can't remember the exact wording of the error message. But yeah, it was something along the lines of 'auxiliary battery malfunction' or 'additional battery defective' – one of those. Besides the alarm acting up, I didn't really notice anything else drastically wrong, just the error nagging me. Honestly, checking for battery drain can be a bit tricky without the right tools. Your best bet is probably taking it to a workshop so they can run a proper diagnostic. They'll be able to pinpoint if something's pulling power when it shouldn't be.

I appreciate your assistance and insights. Based on your experience and advice, I proceeded with the auxiliary battery replacement. The issue is now resolved, and the car alarm system is functioning as expected. The error message has also disappeared from the system memory. It seems the ageing battery was indeed the culprit. Thank you again for sharing your experiences; it was instrumental in confirming the probable cause.