Iron Man simply has more advanced technology than Batman. He has a unique experience with him facing off people like the Hulk. He is an expert at technology. He could easily be able to catch Batman off guard, and kill him. The only way for Batman to win is for him to have a power suit which is highly unlikely assuming that this fight would be between there normal selves.
In addition to possessing the tech, the funds, and the brains, Batman is a superior warrior and athlete. If it came down to fists and no tech, Bruce Wayne would have his martial arts and generally superior fighting skills, while Tony Stark would be left only with snarky commentary, to accompany his beating.