since it runs on Kryptonite you can guess why he needs to get into Batman's lair.
Yeah, as a comic geek, that bit didn't make a whole lot of sense to me, actually. Not the part where Bats has the vault, it's well-known that he's got something handy in case any League member goes dark-side, but come on, this is Lex frelling Luthor we're talking about here. I can't see any way that Superman's worst enemy, the guy who's spent enough time around the green stuff that it gave him Space Cancer, doesn't have at LEAST as big a collection as Batman at this point.
Member of the Super Ethical Genki Hunters [Saints Row the Third]