I just couldn't let it go...

Here's the answer to my own question:

Q: Why Do Battery Letters Skip from A to C? And Was There Ever a B-Cell Battery?
Written by Mental_FlossPublished September 27, 2006

A: Once upon a time, there used to be a B-cell battery. But just like the second sister on the ABC’s Family Matters, the B-cell battery simply found itself written out of the script.
Here’s what happened. Battery letter designations are based on the size of the battery for common sizes. Hence, A is the smallest, and D is the largest. By that same logic, AA batteries are larger than AAA. Unfortunately for B batteries, however, it wasn’t the size that counted.
The fact is, you never see B batteries around because they just aren’t very useful in America. Essentially, the mid-size battery never caught on in products made for consumers, so stores didn’t carry them, and the cycle just fed itself. The truth of the matter is that B-cells, like artsy directors and good jazz musicians, are really only appreciated in Europe, where they’re used primarily for powering bicycle lamps.