Superman is said to be immune and obviously strong but despite that, he has a few weaknesses. He weakens if he is exposed to kryptonite. While uncovered to red sun energy even Kal-El forfeits his strengths. This shortcoming has been a benefit for Batman.
Kal-El can harness the power of the yellow sun that gives him the strengths of being a superhuman. It also gives him a vision of x-ray, speed. He is able to breath cold and can fly high. Whereas Super man’s power originates from the yellow sun. Though red sun can hinder his powers. This power has been used by Caped Crusader as an advantage. Caped Crusader has used this when Batman and Superman have fought against Kryptonian while looking for revenge.
When Superman and Supergirl in Batman/Superman #20 (2015) by ardian Syaf, Greg Pak, Vicente Cifuentes, Mark Morales, Rob Leigh and Ulises Arreola, competes against Kryptonians that are Kela, Tali Zar, Mara Lor-Van… all have been brainwashed by Xa-Du.
Batman’s Red Sun Generator Boosted Superman While Depowering Kryptonians
Xa-Du was the first Kryptonian who was put into the Phantom Zone. During the fight, Superman got hit due to the numerous explosions of heat vision. Then Batman came with a new weapon called Red Sun Generator. He made it as a “superpower suppressor” and told Kara and Kal-El about Martian Manhunter in order to get him a drop from Krypton’s red sun.
This new weapon has proved to be effective as he has achieved in putting down all the Kryptonians. But later he has to drop the rod as he is hit by a heat eruption. All the Kryptonians are set free by Xa-Du from the glass bottle and they have started attacking heroes. Thereafter, Superman takes the Red Sun Generator and takes out all the energy from it. The blast that is caused by this sends Kandorians away. And this depowers all the Kryptonians.
This has turned out to be a winning move. Though, Superman has struggled while using the Red Sun Generator but ultimately, this has helped him win against Kryptonians.