Ba't is the short form of the question word Bakit.
This shortened form Ba't is never used alone.
There has to be some other word after it.
= Ba't ganito?
Why like this?
Bakit ka nandito?
= Ba't ka nandito?
Why are you here?
If you were looking for the translation of the English word "bat"
a bat (club) usually used to hit something or someone
flatulence; a fruit bat
a bat like the ones associated with Batman