2003 RS6 battery not charging but no red battery light

[Robthatch]

Hello, I've got a problem with my RS6. I was jump starting a Golf Gti one day, all fine but when I went to drive off I had a red battery light. So I parked up and did a few checks as you would. Battery was fine but alternator needed replacing. So, I've fitted the new alternator and the battery light has gone out but the voltage read out on the dash is only 12V. It appears the battery is not being charged. Can anyone help me with my dilemma..?
Kind regards,
Robert

[adsgreen]

I'd break out the multimeter and measure a few places

See if the alternator is chucking out good voltage.
Make sure no breaks in the circuit or dodgy grounds.