In Batman #53 (via Screen Rant), Bruce’s emotional state has even driven him to embrace atheism, which wouldn’t be particularly surprising if not for the fact that he should have plenty of empirical evidence at this point that proves God—capital G—definitely exists in the DC Universe. As Bruce explains it in King’s comic, he was raised to be Christian by his parents, but once they were murdered, his faith in everything was shaken until he created the Batman persona and realized that Batman could be something to believe in. Now, though, he’s not even sure if that’s the case, leading him to admit in Batman #53 that he no longer believes in anything.
The catch here is that the DC Universe features a character known as The Spectre who is the physical embodiment of God’s wrath. He has been tasked by God—the God, apparently—with brutally slaughtering bad people on Earth who really deserve it (though the parameters of that are largely left up to whoever happens to be the host of the Spectre entity at the time). Comic book universes get rebooted pretty often, but the incarnation of Batman in King’s books has probably met The Spectre at some point, not to mention the fact that Wonder Woman has connections to various Greek gods, so Batman really should trust that some of these deities really do exist. He may not like it, but saying that he doesn’t believe in any higher power just makes him seem even mopier than usual.