system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Where are all the "B" batteries?
gpt
There was...it was about as long as a D-cell, and a little bit fatter than a AA.

There weren't different enough to find a niche, and didn't catch on like other batteries.  They became hard to find because there weren't a lot of devices that took them, and they stopped making device that took them because their were hard to find.

They were briefly popular in Europe for use in bicycle lamps.