i have an 07 scion with a mechman alt, I don't drop as low as you though. my scion starts at about 14 volts and when it warms up, it stays around 13.3-13.6 volts.
I do drop into the upper 12 volt area, when i don't think i should. The voltage regulation system in the scion suck.
I guess to ask how many runs of wire back for positive, and negative. And what is the size of wire.
I have dedicated power and ground lines to the back 2 runs of 0 gauge each, 2 banks of maxwell caps and nsb 110 ft battery, on a 240 amp alt. I drop into the 12's at around 1800 watts or so...
I mean is it normal in a scion to go below 12.7 full tilt? I dont like reaching 12.5 volts.