I have the same issue. 2000 rx300. Battery died, replaced it with a brand new one, alternator charged intermittently, so I replaced it with a brand new/not remain alternator from start mart. All was perfect throughout the proper break-in process, but on my 1st actual drive the battery is at 11.2v after only 30 miles! All terminals are clean and tightly connected. I'm at a loss here.bad ground wire perhaps?