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Those aren't B batteries, they're "B" batteries. You can tell because there's also a photo of a "C" battery that isn't cylindrical.

The B battery referred to in the article is a vacuum tube battery.

The B battery you linked, is an carbon-zinc/alkaline battery and against that the comment says -

> Most commonly found within a European 4.5-volt lantern battery. Not to be confused with the vacuum tube B battery

This is a latern battery. You put other batteries in it. That's why it's called the 3R12. There are 3x R12 batteries in it.

I remember seeing something like these in roadwork flashing lanterns.