VW Up's Failing Alternator Causes Multiple Power Issues

I had a very similar issue with my 2013 VW Polo with the 1.2 TSI engine. As someone with some experience working on cars, I initially thought it was the alternator causing the problems. The symptoms matched yours exactly, weak starting, dim lights, and electrical system problems. After monitoring the battery voltage with a multimeter, I found the battery health was seriously compromised. The voltage would drop significantly under load. I took it to my regular workshop where they performed a complete electrical system diagnostic. Turns out the original battery was failing and not holding proper charge, causing strain on the entire electrical system. The voltage regulator and alternator tested fine, but the battery was operating well below normal capacity. The fix involved replacing the battery with a new one, plus cleaning all battery connections and testing the charging system. Total cost came to 290€ including parts and labor. After the replacement, all electrical issues disappeared completely. Before suggesting specific solutions for your case, could you share: Has the battery ever been replaced since 2015? What is the actual voltage reading when starting? Are there any warning lights on the dashboard? Have you noticed these issues more in cold weather? This information would help determine if your situation matches what I experienced and provide more targeted advice about the power supply system.

Last service was at 24233km and the voltage readings I took showed 11.8V at startup, dropping to 10.9V when running various electrical systems. I noticed the battery date stamp shows its the original from 2015. The warning lights occasionally flash but nothing stays on consistently. The alternator belt looks ok visually. After reading about your experience and checking the battery health more closely, I am seeing similar voltage drop patterns. Will get the battery properly tested first before assuming its the alternator or voltage regulator. Makes sense to start with the simplest potential fix. The symptoms match almost exactly what you described especially with the dim headlights and struggles during startup. Good to know a new battery solved it in your case without needing more extensive repairs.

Based on those voltage readings, your situation is nearly identical to what I experienced. A healthy battery should show around 12.6V when fully charged and stay above 12V while running. Your readings of 11.8V dropping to 10.9V indicate severe battery deterioration, just like my old Polo had. The original battery lasting 8 years is actually impressive, but those voltage readings confirm its now failing. When my battery terminal connections were tested, the voltage drop across them was minimal, pointing to the battery cells themselves being the core issue. In my case, the electrical problems also started gradually. The battery voltage would sag more noticeably when running multiple systems, exactly as youre describing. The flickering lights and inconsistent warning signals are classic symptoms of a weakening battery unable to maintain stable power supply. Getting a load test done is smart before replacing parts. When I had mine tested, it showed less than 40% of original capacity despite looking fine externally. A quality replacement battery restored proper electrical system function completely. Given the identical symptoms and similar battery age, I strongly suspect youll find the same root cause. Getting voltage readings under load was key to confirming my diagnosis before any unnecessary repairs.

Thanks for sharing those voltage readings, they really help confirm what I was suspecting. Looking at the severe voltage drop from 11.8V to 10.9V under load, plus knowing its the original 2015 battery, I am now quite confident this is a battery health issue rather than alternator or voltage regulator problems. Its good to know your similar case was resolved with just a battery replacement. Those voltage readings are definitely showing the same pattern you experienced with unstable power supply. Having the battery properly load tested makes perfect sense as the next step before replacing any other components. Going to schedule a battery test this week and will likely proceed with replacement given these readings and the battery age. The fact that the problems get worse with longer drives also matches what you described about gradual battery deterioration affecting the whole electrical system. Will update once I get the battery tested and replaced. Really helpful to hear your experience with such similar symptoms, saved me from jumping straight to more complex alternator repairs. The voltage readings were the key diagnostic factor just like in your case.