Afternoon all, wondering if anyone can shed some light on an issue with my dads polo. Recently he has noticed the battery seems to not be charging when the car is running. Its a fairly new battery - taken out the car and given a decent charge and tested to make sure it holds its charge. The alternator has been taken out and taken to a local centre and tested, and we were told its fine.

We have tested the battery in the car with a multimeter and voltage was at 12.6 with ignition off. Start it up and the voltage jumps up to 13.5 or so then it starts dropping and settles around 12.3v. We have tested all the ground points we can see (tested 4 or 5 in engine bay) and they all seem fine. Someone told me to try an ac test from alternator b+ to a good ground and we are seeing 24v ac current. Now to me that would say the alternator diodes are faulty? Just wondering if their are any other tests we can do to see what the problem is as when the 'professionals' tested the alternator they said it was fine.

If its any help its a 02 plate 1.4 petrol engine BBY