S5 Electrical Chaos: Voltage Regulator vs Alternator Battle

I had a similar issue with my 2015 S4 last winter and being somewhat experienced with car electronics, I initially thought it was just a dying battery too. Multiple warning lights, struggled to start, and the diagnostic showed those exact overvoltage warnings you mentioned. After self-testing the battery, I brought it to my workshop since the circuit protection system kept throwing warnings. Turned out the alternator was actually overcharging the battery, causing the voltage spikes and system failures. The complete repair, including parts and labor, cost me 290 Euro. The workshop explained that modern cars with complex electronics are particularly sensitive to voltage fluctuations. In my case, the voltage regulator inside the alternator was failing, causing alternator failure and damaging the battery in the process. To better help diagnose your specific issue, could you share: Is the battery original from 2013? What voltage readings are you getting while idling? Are the electrical issues more noticeable at higher RPMs? Have you noticed dimming headlights or flickering dashboard lights? These details would help determine if your symptoms match my experience with the failing alternator.

Last service was at 126000 KM. Thanks for sharing your experience, as it really aligns with my symptoms. Decided to check the voltage readings while idling per your suggestion, getting 14.8V at idle and jumping to 15.2V when revving, which seems way too high. Definitely noticing dashboard flickering, especially during acceleration. The battery is actually fairly new, replaced it 8 months ago, but these electrical issues started showing up recently. The parallels between your voltage regulator problems and my situation are striking. Will have the alternator checked given these voltage fluctuations. Really appreciate the detailed explanation about the alternator failure connection to the overvoltage warnings.

Our cases sound nearly identical. The voltage readings you shared (14.8V-15.2V) are definitely too high, healthy charging systems typically stay between 13.8V-14.4V. These high voltage spikes from alternator failure explain the multiple system warnings youre getting. When my voltage regulator failed, it also caused similar dashboard flickering during acceleration. The overvoltage condition puts extra stress on all electrical components, which is why youre seeing multiple system failures. Getting this fixed quickly is important, my workshop explained that continuous overvoltage can damage expensive control modules. Your relatively new car battery is also at risk of premature failure from the overcharging, just like mine was. Since the symptoms and voltage readings match my experience almost exactly, Id strongly recommend having the alternator and voltage regulator checked. The repair cost will likely be similar to what I paid (290 Euro), but its worth it to protect the rest of the electrical system. Let us know what the workshop finds. Would be good to confirm if its the same root cause as my case.

Thank you for sharing those voltage readings, they perfectly match what I was experiencing with my alternator problems. After getting these measurements, I feel much more confident about the diagnosis. The car ECU must be getting stressed from these constant power surges, which explains all the system warnings. Based on the similarities with your case, I will schedule a workshop visit this week. Rather than risk damage to the electrical components and my fairly new car battery, getting the alternator and voltage regulator checked seems like the smart move. The 290 Euro repair cost you mentioned is actually lower than I expected given all the symptoms. Will definitely update once I get it looked at. Really appreciate the detailed explanation and troubleshooting help. Seems like overvoltage issues with these models often trace back to alternator failure, so hopefully addressing that will resolve all the electrical gremlins.