where does the term old bat come from?

Answer 1

I'm going to guess it's because older women were more likely to be widowed, and often would wear black from that point forward, and if someone (usually a son-in-law) didn't care for their opinion or intrusion, they called them an "old bat" because bats (the mammal) were usually black and annoying.

Answer 2

my mother in law is the origin of the term...lol.