Audi A5 Engine Stalling Points to Multiple Issues

I had nearly identical issues with my Audi A4 2016 last year. Having some experience with auto electrical systems, I first suspected a simple battery problem too. The symptoms matched exactly, unusual engine stalls, warning lights, and the start-stop system completely stopped working. The car battery was indeed the root cause, but not in the way I initially thought. The original battery had degraded to a point where it couldnt properly support the start-stop system and other electronic functions. The workshop diagnosed a heavily discharged battery that was also showing signs of internal damage. They performed a full electrical system check to rule out charging issues. The repair involved replacing the battery with a higher capacity AGM unit and recalibrating the start-stop system. Total cost was 290 Euro. After the fix, the automatic restart function worked flawlessly again, and all warning lights cleared. No more unexpected engine stalls since then. To help diagnose your specific case, could you share: Current battery age, Any recent electrical issues, Whether eco mode still functions, Specific error codes stored, If the problems started gradually or suddenly

Thanks for sharing your experience. I also noticed these issues starting after my last service at 54757 KM. The starter motor seemed sluggish before the engine stalling began. The error codes from my diagnostic scan point to voltage issues, so your battery replacement solution sounds promising. What concerns me is that my start-stop system completely failed before other symptoms appeared, which might indicate a different root cause than a standard car battery problem. Did your repair shop mention if the engine stalling could be linked to a faulty alternator? That might explain why replacing just the battery fixed everything in your case. The 290 Euro fix seems reasonable if it solves all these issues.

Thanks for the additional details about your A4. Based on your description of the starter motor acting sluggish and the voltage-related error codes, my experience matches closely with what you are seeing. When my start-stop system failed, it was actually the first warning sign before the engine stalling began. The workshop explained this is a common protective measure, the start-stop system shuts down first when battery voltage drops below critical levels to prevent damage to the electrical system. The alternator was thoroughly tested during my diagnosis and was working perfectly. The battery management system in these models is quite sensitive, and a weakened battery alone can trigger multiple fault codes that seem like alternator issues. The sluggish starter motor behavior you mentioned is another classic symptom of a failing battery rather than alternator problems. My 290 Euro repair included a full electrical system test that confirmed the alternator was fine. Given your identical symptoms and the fact that issues began post-service, a battery replacement will likely resolve your problems too. The key is using the correct AGM battery specification to properly support the start-stop system functionality. If you want to verify before replacement, most auto parts stores can test both your battery and charging system for free.

Thanks everyone for the detailed responses. Your explanations about the battery management system and start-stop behavior really helped clarify things. I scheduled an appointment to have both the battery and charging system tested tomorrow. The symptoms match exactly what was described, especially how the idle stop system failed first, followed by engine stalling and those voltage-related error codes. The 290 Euro repair cost seems worth it if it fixes all these issues. Better safe than sorry with electrical problems, and I need my car working reliably. Will make sure they use the correct AGM battery spec to avoid any compatibility issues with the start-stop system. Will update once I know what my shop finds during testing. Hoping its just a simple car battery issue like yours was and not something more serious with the alternator or electrical system.