Dash lights upon start

Hey guys, so this morning i started my 2004 tdi jetta and once it started my battery, airbag and abs lights all came on. Once i let my car idle for 2ish minutes, they all turned off. Its worth mentioning that the battery light regularly comes on ever since my dad replaced my alternator a few months ago, but it goes off after a few minutes idling usually.
Any ideas/help would be appreciated!

Your dad probably used a crappy refurbished alternator (1) or failed to firmly secure the connections (2).

if it's the problem No 1, then it sounds like the rectifier is faulty.
In case it's No 2 issue, then check the connections, clean them and retighten.

Or possibly a failing cell in the battery . . . have it load tested as well . . .

- Tim