It's likely a misunderstanding or a made-up term. Perhaps you're thinking of:
* A bat dog: These are dogs specifically trained to assist people with disabilities, particularly the visually impaired. They are not bats.
* A dog that likes to play with bats: Some dogs might enjoy chasing after toy bats or even real bats (although that's not recommended as it can be dangerous).
Could you tell me more about where you encountered this term? That might help me figure out what you're looking for.