What are A or B Batteries?

We all use “AAA”, “AA”, “C”, and “D” batteries. I heard today that there was a “B” battery and wanted to find out what that was about. In my initial research, I also saw there was an “A” battery, too.

The “A” battery is used to provide power to the filament of a vacuum tube^[1]. It is sometimes colloquially referred to as a “wet battery”. (A dry cell could be used for the purpose, but the ampere-hour capacity of dry cells was too low at the time to be of practical use in this service.) The term comes from the days of valve (tube) radios when it was common practice to use a dry battery for the plate (anode) voltage and a rechargeable lead/acid “wet” battery for the filament voltage.

“A” batteries were initially 2 volts, being lead acid accumulators, but with the introduction of all dry battery radios, 1.4 volts became more common. Other voltages can be encountered.

The “B” battery is used to provide the plate voltage of a vacuum tube. It is sometimes colloquially referred to as a “dry battery” (although there’s no reason why a “wet” battery of suitable voltage couldn’t be utilized for the purpose). The filament is primarily a heat source and therefore the “A” battery supplies significant current and rapidly discharges. The “B” battery experiences comparatively little current draw and retains its stored capacity far longer than an “A” battery.

Early “B” batteries used with bright emitter tubes were 120 volts, but these quickly became obsolete as they were replaced with examples having voltages of typically 45 volts, 67½ volts, or 90 volts as more efficient tubes became available

In 1924, the naming system became standardized to keep things uniform as technology continued to flourish. The system used to be based on numbers, and when the alphabetic system was adopted, there was one straggler from the old system in the form of the No. 6 battery. In the new system, as the alphabet progressed, the batteries would periodically get larger and larger. So, at one point, the now largely out-of-use.

“A” batteries were the smallest available. “AA” and “AAA” were added to the system to denote the two newer battery sizes that were smaller than the “A”. “B” batteries, and “A” batteries, for that matter, stopped having a lot of practical uses, so they largely went out of vogue.

“B” batteries are still sometimes used in Europe for lanterns and bicycle lamps. According to Energizer, though, their popularity is dwindling there, too, and they might be completely discontinued.