Again, Superman does not go into battles thinking he can lose. Before Doomsday, the thought of him dying was pretty laughable.
This is why Batman beats Superman. To Superman, Batman is just a man in a bat costume fighting crime. True, but Batman is much more than that. A master tactician, martial artist, detective, and hell he's pretty damn good when it comes to creating thing like technology and gadgets. If anything, Batman, a Batman who has been doing this for 20 years? They didn't do HIM justice in this movie.
It makes total sense for Superman to rush into a fight against Batman not knowing the concept of "Prep Time." Superman realistically lost the fight when he ran into Batman at the warehouse and told him to not be Batman anymore.
If you encounter Batman ONCE and you let him live, you have effectively removed yourself from ever getting a W on him.
That's why Superman loses when he faces Batman. Supes is'nt a killer, does'nt believe he himself can be harmed, and does'nt understand how crazy Batman is.
It's also why in the end, Batman is the one that Superman trusts that large piece of Kryptonite to...and Superman is naive enough to think that it's the only piece Batman has