Update
I charged battery with agm battery charger over night and also switched ground to 4 gauge wire ( not stock, knu wire) and light's still dim.
Also, I build a new box and now have a bad voltage drop, lowest I saw was 11.5. On average, it stays around 12.5 and 13-13.3 while driving.
So I'm guessing only way to fix it is to get high output alternator? Or add another battery?