I said it. Let's say, we're talking about the New 52 Superman, and the incarnation of Batman that gives him the greatest advantage (whatever that may be).
Batman has 6 months prep-time, and advantage that Superman doesn't have.
Superman has no idea they are going to fight. Both sides are only allowed to kill each other, no one else.
Batman has all the Kryptonite he wants.
There is still no way Batman will win. Zippo chance. Nothing. Prove me wrong.
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Batman acts all friendly like to Supes while secretly poisoning him with krypto for the 6 months leading up to the fight. By the time Batsy makes his move Supes won't even be able to get out of bed.