Audi S3 Battery & Charging System Nightmare

Had similar electrical problems with my 2010 Audi A3 2.0 TFSI. The symptoms matched exactly, slow cranking, flickering lights, and unusual electrical failures. Initially thought it was just a battery issue, but voltage drop testing revealed more problems. The main cause was a failing alternator not properly charging the battery. The voltage regulator inside the alternator was malfunctioning, causing inconsistent charging. The battery terminal connections were also corroded, making the charging problem worse. The complete fix required: New alternator installation, Battery terminal cleaning and replacement, Full charging system diagnostic, Battery replacement due to damage from irregular charging This was a serious electrical problem that needed immediate attention. Continuing to drive with these symptoms risks leaving you stranded and can damage other electrical components. The alternator issue was causing the battery to be heavily discharged, which explained why temporary fixes didnt last. Recommend getting a proper charging system diagnosis. Simply replacing the battery might mask the underlying alternator issue, as happened in your previous repair attempt.

Thanks for sharing your experience. Same symptoms hit my S3 last winter, unusual electrical glitches and starting problems due to low voltage. The battery voltage reading was all over the place. The shop found corroded battery terminals and a failing alternator. Good thing I got it checked when I did, as they said more electrical problems would have followed. Curious what the repair cost was in your case? Also wondering if youve had any electrical issues since the fix? Would be helpful to know if its been reliable for you, as Im considering doing some preventive maintenance on my alternator soon.

Thanks for asking about the follow-up. After getting the repairs done, all the low voltage issues and electrical problems have completely cleared up. The undervoltage warnings disappeared and havent returned in months. The total repair came to 290 Euro for diagnosing and fixing the battery health issues. The original battery was heavily discharged beyond recovery, so replacement was necessary. The technicians also cleaned all connections to ensure proper power supply. My alternator actually tested fine during the diagnosis, unlike yours, so I lucked out there. No electrical problems since the fix, starts instantly every time, all systems working perfectly. The steady voltage readings confirm the charging system is working as it should. If your alternator is showing signs of wear, preventive maintenance is smart. A failing alternator can quickly lead to battery damage and broader electrical system issues. Much better to address it early than risk getting stranded with a complete failure.

Thanks for the input. Finally got my S3 sorted after the electrical problems were driving me crazy. Took it to a trusted mechanic who did a complete power supply diagnosis. The charging system was indeed the culprit. Found a failing alternator and severely corroded battery terminals. Total bill came to 780 Euro including parts and labor. More than I wanted to spend, but the alternator replacement was inevitable. Been running perfectly for the past month now. No more flickering lights or starting issues. Battery voltage stays steady and all electrical systems work normally again. The mechanic mentioned I caught it just in time before it could damage other components. For anyone facing similar symptoms, dont wait around hoping it fixes itself. A proper diagnosis saved me from potentially bigger problems down the road. Really glad I got it sorted before winter hits. Thanks again for helping me understand what I was dealing with. The advice here helped me ask the right questions at the shop.