dumb people and dual batteries

a friend of mine just installed a second battery for his system (now runing 2 yellow top optimas) he didnt upgrade the alternator (85 amp) out of a toyota ran his system with the truck off, and it died. hes pissed, i told him to upgrade the alternator cause the 2 batteries wont do shit, now can soemone else back me up? or am i way off thanks