Board Thread:Versus Debates/@comment-28731007-20160624040357/@comment-26773508-20160625160458

Agreed with @Thekillman. Kakashi lost his power only after Obito left his body, once the battle was decisively over. There is no suggestion in the manga that Kakashi tired out. Rather, Obito simply decided to go back to making out with Rin in the spirit world once he verified that he was no longer needed. Had the battle against Kaguya lasted longer, I'm sure Obito would have stayed longer.