RS5 Battery & Alternator Issues Causing System Failures

My 2016 S5 showed nearly identical symptoms last winter. The initial circuit protection warnings and electrical issues pointed to alternator failure, but diagnostics revealed a failing voltage regulator combined with a degraded car battery. The battery showed heavy sulfation and could no longer hold proper charge. This caused a cascade of electrical problems, sporadic ECU warnings, difficult cold starts, and unusual system failures. The voltage fluctuations were stressing multiple electrical components. The fix required: Complete battery replacement, New voltage regulator, Full electrical system diagnostic, ECU reset after repairs The original alternator was actually fine, but the unstable power delivery from the bad battery had triggered multiple fault codes. After replacing these components, all electrical issues disappeared and the car has been running perfectly. Given your symptoms, particularly the overvoltage warnings and starting problems, this sounds like a serious electrical issue that needs immediate attention. Continuing to drive with these problems risks damaging other electrical components. The parallel symptoms between our cases suggest you should have both the car battery and voltage regulation system thoroughly tested rather than just replacing parts one at a time.

Thanks for explaining your experience with similar electrical issues. My repair was completed about 3 months ago and everything is working perfectly now. The car electronics are all functioning normally with no more overvoltage warnings or starting problems. Curious, do you remember roughly how much you paid for the full repair? Also has your car shown any new electrical gremlins since fixing those components? Mine cost me around 1200 Euro for parts and labor but prices seem to vary quite a bit.

Thanks for the update about your RS5. Since my repair at roughly 290 Euro for the battery replacement, my S5 has been completely stable with no electrical issues whatsoever. The voltage regulator check was actually included in the diagnostic service. The car ECU is now free of any fault codes and the circuit protection system works as intended. Once they addressed the heavily discharged battery, all the overvoltage warnings cleared up permanently. Your repair cost seems higher, but it likely included additional components or labor that my fix didnt require. Running strong for 3 months now with zero electrical issues or warning lights. The stable power delivery from the new battery has kept all systems working perfectly.

The repair trip turned out much better than expected. After getting a second opinion from a different shop, they quickly diagnosed the root cause, a failing voltage regulator and severely degraded battery that was causing power surges through the electrical system. The fix was comprehensive: New AGM battery installation, Voltage regulator replacement, Full system diagnostic scan, Clearing all fault codes Total cost came to 1200 Euro which included parts and about 4 hours of labor. The car ECU is now working flawlessly with no more overvoltage warnings or starting problems. All electrical systems are functioning normally again. Looking back, I wish I had addressed the battery issues sooner before they cascaded into multiple system failures. The circuit protection was clearly trying to warn me through those initial fault codes. At least now I know to take electrical warnings seriously rather than hoping they will resolve on their own. Very happy with the results after 3 months, no more electrical gremlins or warning lights. The stable power delivery has kept everything running perfectly.