I ran stock alt with the Big3 in 1/0 along with a pair of Batcap 2000's pushing about 5Kw rms daily and never dropped below 12.8v~. Added an O.G. 300A alt and never dropped below 13.6 (modded the alt to put out 15.5v~)
now I sold that stuff and am running about half that power on the O.G. alt and the Big3 alone dropping to about 12.6~ at full tilt. I will be adding a small battery soon.