VW Polo Battery Issues: Failed Alternator Alert

As someone with some experience working on cars, I had a very similar electrical problem with my 2014 VW Golf. The symptoms you describe match exactly what I encountered, slow cranking, dim lights, and failing electronics all pointed to a charging system issue. After experiencing these alternator issues, I took it to a workshop. They ran a full diagnostic on the charging system which revealed a heavily discharged battery that was beyond recovery. The voltage drop was severe enough that even after jump starts, the system couldn't maintain proper charge. The fix in my case was straightforward, a complete battery replacement along with testing of the alternator and charging system to ensure no underlying electrical problems. Total cost was 290€ including diagnostics, parts and labor. Before suggesting the same solution for your Polo, it would help to know: How old is the current battery? Have you noticed any warning lights on the dashboard? Does the battery warning light stay on while driving? What voltage reading are you getting when the engine is running? This information would help determine if you are facing a simple battery health issue or if there might be deeper problems with the charging system that need attention.

Last service done at 103347km, wanted to share some updates on my issue. Had my multimeter check the battery terminal readings. While idling it shows 12.1V which drops under load, definitely not the 13.5-14.4V it should maintain. Also noticed some corrosion on the terminal connections. After cleaning the battery terminals thoroughly and rechecking the power supply readings, there was only minimal improvement. The voltage drop persists despite the clean connections, pointing to a likely charging system failure rather than just surface issues. Got a quote for both scenarios, battery replacement at 180€ or full alternator repair around 450€. Going to have the charging system properly tested before deciding which route to take.

Thanks for the voltage readings, they really confirm what I suspected after dealing with similar issues on my VW. That 12.1V at idle is a clear red flag, as a healthy charging system should push close to 14V when running. When I had my Golf fixed, the alternator issue showed almost identical symptoms and voltage patterns. The battery terminal corrosion you found is worth noting but like you discovered, cleaning only helped marginally. In my case, what looked like a simple battery problem turned out to be a failing voltage regulator inside the alternator. The repair shop explained that when the regulator starts failing, it cant maintain proper charging voltage, leading to those exact symptoms youre seeing. Before spending on a new battery, definitely get the alternator tested. My mistake was replacing the battery first only to find out two weeks later that the alternator was the root cause. The voltage regulator failure meant the new battery wasnt getting properly charged either. If the alternator testing confirms a fault, that 450€ quote sounds about right based on my repair costs. While it's steeper than a battery replacement, fixing the actual cause will save money long term and prevent damage to other electrical components.

Had the workshop do a full diagnostic test today. Voltage regulator in the alternator was indeed failing, causing battery drain and all those electrical problems. Their tests showed 11.9V while running, way below normal charging voltage. Since the battery had been repeatedly discharged due to the bad alternator, they recommended replacing both components to prevent future issues. Total repair came to 630€, not cheap but at least all the electrical problems are sorted now. The engine cranks properly, lights are bright and stable, and voltage readings are back to normal at 14.2V while running. Good thing I had the full system checked instead of just swapping the battery. Really appreciate everyone sharing their experiences, especially about checking alternator health first. Would have wasted money on just a battery otherwise. Time will tell, but the car feels completely back to normal now.