Warning: Spoilers for Batman/Superman: World's Finest #1 Ahead!
The victor of a fight between Batman and Superman has been a constant debate amongst the comic community, and a new team-up comic with the two heroes has proven that Batman can't beat Superman even with kryptonite. The long-held debate is rooted in the classic "brains vs. brawn" question. While Superman may have the strength to take down Batman, there have been arguments that Batman's wit and detective skills could help him come out on top. This has been a battle that's been speculated on for so long that it's made its way into the comics with The Dark Knight Returns and the movies with Batman v. Superman: Dawn of Justice and very few have truly answered the age-old question...until now.
The first issue of Batman/Superman: World's Finest by Mark Waid and Dan Mora show the Man of Steel and the Dark Knight teaming up together to take down Poison Ivy in Metropolis when a surprising foe shows up. Metallo, armed with a kryptonite core, is able to get close enough to Superman to inject him with a liquid form of red kryptonite. While it flows through his veins, Superman's powers are constantly mutating to the point that he's seeing his greatest enemies when they aren't there, burning at extreme degrees and even turning to steel. It's during this battle that Batman realizes that he's hopelessly outmatched.
While Superman is seeing illusions of villains like General Zod and Lex Luthor, Batman realizes that Superman is in a dangerous state. He's causing so much destruction that no one superhero could take him down. However, while one superhero can't take Superman down, Batman comes to realize that teaming up with the Doom Patrol will put a stop to Superman's unintended rampage. Enlisting the help of Negative Man, he manages to talk Superman down to get him to a calmer state before having Negative Man use the radiation emitting from Superman to replicate the radiation of a red sun, thus making Superman powerless. Batman alone can't put a stop to Superman. If he had taken on the Man of Steel one-on-one, he would surely be clobbered. Unless he had a Red Sun Heater in his utility belt, there was no way he'd be able to subdue Superman had the Doom Patrol not showed up.
This puts into perspective just how small Batman can be when going up against a character like Superman. Yes, he can have time to prepare for a battle, but this is a situation that even he didn't see coming. He thinks quickly to get Negative Man's help, but it comes at the cost of him knowing he can't win this battle alone. Even if he had some kryptonite gas on him, he likely wouldn't have been able to stop Superman because the gas has been shown to only work temporarily. He knows that Superman would just knock him out cold, and it even shows when he has his plan at the ready and tries to convince Clark that what he is seeing isn't real. Instead of taking him on with fists, he instead uses words to reach the Superman he knows to get him where he needs him in order for Negative Man to do his thing.
While this isn't necessarily a diss on Batman's detective skills, which is certainly where he thrives, Batman/Superman: World's Finest does show the mortal limits that Batman has when confronting the Man of Steel. He can try to take him on, but there are certain moments where even he would need to call for help because he would never be able to finish the fight on his own. It just goes to show that teamwork is where Batman can succeed, and even if he has kryptonite, Batman needs other people if he ever wants to beat Superman in a fight.