VW Fox Electrical Issues: Bad Battery vs Alternator Fix

I had a similar issue with my 2006 VW Polo diesel last winter, and having dealt with several electrical problems before, I can share some relevant experience. The symptoms you describe strongly point to a charging system problem. My car showed identical signs, weak starting, dim lights, and failing electronics. The voltage drop was severe enough to trigger multiple dashboard warnings. After taking it to my regular workshop, they performed a thorough charging system diagnosis. Tests revealed the battery voltage was extremely low and unable to hold a proper charge. They also checked the alternator output and found it was working correctly. The final bill came to 290€ which covered: New battery installation, Full electrical system diagnostic, Battery terminal cleaning and service Before suggesting specific solutions for your Fox, could you share: How old is the current battery? Does the battery warning light come on while driving? Have you noticed any unusual alternator noise? Did you recently install any additional electrical accessories? This information would help determine if your case might need a different approach, as power supply issues can stem from various sources in the electrical system.

Just had my 13344km service last month and wanted to follow up. Really appreciate the detailed response. The battery is 5 years old, and yes, the battery warning light flickers occasionally while driving. No unusual alternator sounds that I can detect. Your experience matches mine exactly, the voltage drop is most noticeable during cold starts. Had the voltage regulator tested yesterday at a local shop. The readings were way below spec, fluctuating between 12.1V and 13.2V at idle. The technician mentioned the alternator might still be okay, but the voltage regulator is likely failing. Think I will go ahead with the repair since these electrical problems are getting worse. Just hoping the fix is as straightforward as your case and doesnt require a full alternator replacement. Would you recommend replacing the battery at the same time? Given its age and the recent power supply issues, it might make sense to do both.

Thanks for the voltage test results, those numbers definitely confirm a charging system problem. Going by my repair experience, replacing both the voltage regulator and battery is the smart move here. My old battery was about the same age when it failed, and the weak charging from the faulty regulator had accelerated its deterioration. The low voltage situation creates a cycle where the battery gets more stressed trying to compensate. The repair shop found my alternator was fundamentally sound once they swapped the regulator. Total cost ended up around 380€ for both parts with labor. The technician explained that voltage regulators often fail before the alternator itself, which matches what your shop is saying. Since fixing it, all those electrical gremlins disappeared, strong starts, bright lights, and stable system voltage. Would definitely suggest doing both components at once rather than having to go back for the battery later. Just make sure they do a full charging system test after the repair to verify the alternator is producing proper voltage. Mine now holds steady at 14.2V at idle, which is exactly where it should be.

Thanks to everyone who replied! Just wanted to update the thread after getting everything fixed. Took your advice and replaced both the voltage regulator and battery. Total repair came to 410€ including parts and labor. The power supply issues have completely resolved, no more voltage drop during starting and all electrical systems are working perfectly. The shop confirmed the alternator itself tested fine after installing the new regulator. Battery health is now showing excellent readings with proper charging voltage at 14.4V. They also cleaned all battery terminals as a precaution. For anyone searching the forum with similar symptoms: the flickering battery warning light combined with the unstable voltage readings were the key indicators of the failing voltage regulator. Getting both components replaced at once saved me a second trip to the shop. Really glad I checked here before assuming I needed a whole new alternator. Much cheaper fix in the end. The car starts instantly now and all those electrical gremlins are gone.