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 would win. If he's got all the Kryptonite he wants he'd just sneak into the Fortress of Solitude while Superman was out and plant Kryptonite in his food and water, then kill Superman with a giant strap-on made of Kryptonite.