Silly and slightly crazy and behaving in a confused way. (Cambridge Dictionary)
Of, relating to, or resembling a bat. (Merriam – Webster)
Mentally unstable: Crazy. (Merriam – Webster)
Mad; insane. (Oxford Dictionaries)
If you say that someone is batty, you mean that they are rather eccentric or slightly crazy. (Collins Dictionary)
Crazy (or What Is It Like to be Batty?)
Crazy In Love – She’s Simply Batty About That Clown!