Please be extremely cautious in immediately accepting as some websites suggest that the appearance of a black bat in a dream is necessarily a premonition of a personal disaster (white bats are seen by some as predicting the death of a family member).
All of this seems extremely negative to me, and does not allow for the fact that what a black bat means to your dreaming mind may be completely different from somebody else's.
Basically a black bat in a dream could mean anything, although whether it is regarded as being mainly positive or overall negative largely depends on in which country or culture you dreamed of it or them.
In China for example, the bat is a symbol of good luck and happiness. If you find bats very scary they will likely not mean the same to you as to someone who regards them as blessed bringers of change.
Also the colour black does not always necessarily translate into being something negative or evil, unless it appears completely on it's own. When mixed or associated with other colours it modifies their own generally accepted interpretations meaning e.g. darker shades of red, blue yellow, etc..
What therefore were the other most dominant colours in your black bat dream?