If idle charging is the issue then change the alternator pully to be smaller diameter.
Many of the repo have a 3" pulley when a 2.5" is what the stock pulley was.
Disclaimer....
Your crank and alternator pulley diameters need to be matched so the alternator is spinning the correct rpm at a given engine rpm
With a 6 to 6.5 crank and a 3 alt, it's too slow. But with a 2.5 it's fine.