Assuming you’re talking about those cute videos of bats being fed bananas while being nursed back to health. Every video I’ve seen was of a fruit bat which eats… fruits. Bananas, mangos, dates, avocados, and any type of pulpy fruit. Peeled bananas are probably easier to feed to them than say an avocado. They just happen to look adorable doing it.
So short answer that’s the kind of foods that type of bat eats. Other kinds of bats (arguably less cute kinds of bats) prefer things like insects.