Audi S6 Charging Nightmare: Battery vs Alternator Fix

Had similar voltage issues with my 2009 Audi S4 last winter. The symptoms matched exactly, weak starts, dimming lights, and electrical system irregularities all pointed to a failing charging system. The low voltage problem turned out to be more complex than just a weak battery. After testing, we found significant voltage drop across corroded battery terminals and a failing voltage regulator in the alternator. The battery voltage reading showed 10.8V while running, far below the normal 13.8-14.2V range. The repair required: Complete alternator replacement, New battery terminals and cables, Battery replacement due to permanent cell damage This was a serious repair job that took several hours. The original alternator failed because of a worn voltage regulator, which then caused the battery to discharge repeatedly until it was damaged beyond recovery. Key checks before repair: Test battery voltage both at rest and running, Check for voltage drop at battery terminals, Have alternator output tested under load, Inspect all charging system ground connections These issues typically cascade, one component fails, damaging others in the process. Getting it diagnosed correctly the first time prevents repeated repairs.

Thanks for your detailed response on the charging system issues. Your situation sounds nearly identical to what I am experiencing with my S6. Getting both the alternator and battery replaced at once makes total sense given how the power supply components are interconnected. Quick follow up, can you share approximately how much the complete repair ended up costing? Also wondering if youve had any recurring battery voltage problems since getting everything fixed? I want to make sure I budget appropriately and find a shop that will address the whole charging system rather than just replacing parts one at a time.

Good news, since getting my S6 properly repaired, the electrical problems have been completely resolved. The undervoltage detected warning disappeared and hasnt returned in months. The shop did a thorough job fixing the heavily discharged battery, which was the core issue causing the cascade of electrical problems. The total repair came to 290 Euro including parts and labor. This covered a new battery, cleaning the battery terminals, and testing the entire charging system to ensure everything was working correctly. While it wasnt cheap, addressing the complete charging system rather than just replacing individual parts prevented further issues down the line. The voltage readings are now consistently in the normal range, and I havent experienced any more problems with dim lights or weak starts. A proper diagnosis and repair of the low voltage issue was definitely worth the investment.

I finally got my S6 fixed last week and wanted to close the loop on this thread. Found a specialized shop that really knew what they were doing with the charging system diagnostics. My repair ended up being pricier at 850 Euro since they found the voltage regulator was completely shot and had damaged the alternator. They replaced both, plus installed a new battery and cleaned all terminals. The mechanic showed me the worn components and explained how the failing parts had created a chain reaction of electrical problems. The difference is incredible, strong starts, bright lights, and all systems working perfectly now. The battery voltage stays steady at 14.2V while running. Definitely worth paying more for a thorough fix rather than the band-aid solution my previous mechanic attempted. For anyone facing similar symptoms, invest in finding a shop that specializes in electrical diagnostics. Having someone who understands the whole charging system saved me from doing multiple repairs.