2003 A4 1.9TDI Alternator

[AC123]

Hi

A few days ago the battery light flickered on in my A4. Since then it is now on all the time.

This to me points to the battery not charging, and hence the alternator?

I've done a bit of a google and read something about an alternator clutch? Am I better just changing the whole alternator?

This is a video of it:

The screwdriver can just stop the internal spinny thing (the technical term for it).

Any help appreciated.

Thanks