VW Lupo Electrical Issues Point to Charging System

Having experienced similar battery voltage issues with my 2006 VW Polo diesel, I can relate to these symptoms. With some experience working on VWs, this sounds very familiar. The symptoms you describe, slow cranking, dim lights, and intermittent electrical failures, are exactly what I faced. Initially thought it was just low voltage from a bad battery, but the workshop discovered multiple issues during testing: 1. Battery terminal connections were corroded 2. Alternator output was below spec 3. Ground strap had deteriorated The complete fix cost 290€ and included: Cleaning and protecting battery terminals, Replacing the alternator, Installing a new ground strap, Full electrical system diagnostic The power supply issues disappeared completely after these repairs. The alternator was actually the main culprit, not providing proper charging voltage to the battery. Could you share: Battery voltage readings while engine running? Any warning lights on the dash? Have you noticed issues particularly during cold starts? Does the battery light stay on while driving? This information would help determine if your issue matches what I experienced with my Polo.

Latest service was at 117000km and included timing belt replacement. Your symptoms match my previous experiences with failing alternators. I had my battery tested which showed good health but low charge. When checking voltage drop across terminals, I found 14.1V at idle but dropping to 12.8V under load, indicating the charging system wasnt keeping up. A voltage test across the battery terminals while running different electrical loads (headlights, AC, etc) should help identify if the alternator is the culprit. The battery light occasionally flickers on cold starts which also points to charging system problems. Let me know what voltage readings you get, this will help determine if you need the alternator replaced or if its just connection issues.

Thanks for sharing those details about your voltage readings. I see you're getting similar alternator issue symptoms to what I experienced with my Polo. The voltage drop under load you mentioned matches exactly what happened with mine, the alternator just couldn't maintain proper charging when electrical systems were running. When I did voltage testing on my car, the readings started at 14.2V at idle but dropped below 13V with loads, which wasnt enough to maintain battery voltage. The flickering battery light on cold starts was also an early warning sign I initially ignored. A few quick tests you can do: Check voltage at battery terminals while revving to 2000 RPM, Monitor voltage with headlights and AC running, Test for voltage drop between alternator and battery The power supply problems will likely get worse without fixing the root cause. In my case, even after cleaning all connections and replacing the ground strap, the alternator still needed replacement to resolve the charging issues completely. Based on your readings and symptoms, sounds like you might be facing the same alternator replacement I needed. The repair costs may be similar to what I paid (290€) for the full fix.

Based on your detailed testing experience, I'll follow up on those voltage readings. Today I hooked up my multimeter and found even worse numbers, idle voltage now drops to 13.8V and goes as low as 12.5V with electrical loads running. The battery health still tests good but the charging system definitely isnt keeping up. I methodically tested the voltage drop across each major connection point. While the battery terminals and ground strap connections show minimal resistance, the alternator output is clearly struggling. Even at 2000 RPM, it cant maintain proper charging voltage with the headlights and AC running. The battery light now comes on more frequently during cold starts and stays lit longer. Given these failing charging system symptoms match what you experienced, I think its time to bite the bullet and replace the alternator before getting stranded somewhere. The 290€ repair cost seems reasonable considering the comprehensive fix you got. Thanks for sharing your diagnostic process, it helped confirm my suspicions about the alternator being the root cause rather than just bad connections or a weak battery. Will schedule the repair this week before the power supply issues get any worse.