Batman has adopted the role of Green Lantern a handful of times. However, the most notable example features in the one-shot Elseworlds tale, Batman: In Darkest Knight. Published in 1994, this comic follows the basic tenets of Batman mythos, such as the murder of his parents.
The largest shift occurs with Bruce Wayne’s becoming a Green Lantern, instead of Hal Jordan.
Desperately wanting to fight crime, Bruce begs for a sign about the best course of action. A sign arrives as a crashed alien vessel, where an injured Abin Sur relinquishes his Green Lantern Power Ring and gives it to Bruce. In one issue alone, Bruce proves an effective Lantern.