My son has just come in "the battery light is on " doesn't seem to be too worried/ aware it may just die on him at the most inconvenient time/place. Voltage over terminals is 12.02v dropping to 11.6 with the engine ticking over and revving. Is it new alternator time? is there anything else that could be the cause?. It's a polo. Thanks
Should increase voltage to about 13.5 volts at around 2.5K revs otherwise its not charging the battery.
Check all wiring and the aux belt before going down the replacment route.
Sorry to state the obvious but is the aux drive belt still there?
If so then first thing to check are the earth points and alternator wiring.
Then it's either the alternator, regulator or maybe (clutching at straws as I don't know if this will manifest like this) a faulty battery pulling the voltage down?
Make sure you have any codes for the radio etc before disconnecting the battery.
Good point. Disconnect battery and check that all cells are functional. Should read around 12v disconnect. If less then could be a faulty cell/plate
The belt is on,one of those micro v flat ones and the battery is quite new. Any other tests to do?
check earthing points.
check output at alternator.
If you need to replace consider a reconditioned alternator. Many places will take your old one and sell you a tested and reconditioned one for much less than a new alternator.