B batteries absolutely existed, and they were once common. You’ve never seen one because the devices that needed them disappeared, and the battery size fell out of consumer use by the mid-20th century. The letter designations for batteries (A, AA, AAA, C, D) come from an older naming system, and B simply lost its place on store shelves as electronics evolved.
What B Batteries Were For
In the early days of radio, vacuum tube sets needed multiple batteries to operate. Each battery handled a different job inside the circuit, and they were labeled A, B, and C. The A battery heated the tube’s filament. The B battery supplied plate voltage, which was the higher voltage needed to amplify the radio signal. The C battery provided a smaller bias voltage to fine-tune performance.
Early B batteries were large and powerful, starting at 120 volts for the first generation of vacuum tubes. As tube technology improved, the voltages dropped to 45, 67.5, or 90 volts, with some models offering taps every 22.5 volts so users could select the voltage they needed. The last B batteries manufactured were 22.5 volts and roughly the size of a modern 9-volt battery. They were purpose-built for a technology that no longer exists in consumer products.
How Battery Letter Names Work
The American National Standards Institute (ANSI) assigned letter codes to battery sizes, with the letters essentially acting as arbitrary labels for different physical dimensions. “D” is the largest common cylindrical cell, “C” is the next size down, and “AA” and “AAA” are progressively smaller. The “B” size sits between A and C in this system, measuring 21.5 by 60 millimeters. It’s a real, standardized size. It just isn’t one that manufacturers build devices around anymore.
The international system (IEC) works differently, using letters and numbers to encode a battery’s chemistry, shape, and exact dimensions. A CR2032 coin cell, for example, tells you it’s lithium chemistry, round, 20 millimeters across, and 3.2 millimeters thick. In that system, “B” doesn’t refer to a size at all. So depending on which naming convention you’re looking at, B either means a specific (obsolete) cylinder size or a chemistry code for something unrelated.
Why B Batteries Disappeared
Once home radios switched from battery-powered vacuum tubes to plug-in models and then to transistor radios, the original reason for B batteries vanished. Transistor electronics needed far less power and used smaller cells. Manufacturers designing portable devices in the second half of the 20th century gravitated toward AA, AAA, C, D, and 9-volt batteries because those sizes hit the sweet spot of energy capacity, physical size, and cost for the products people were actually buying.
The B cell’s dimensions didn’t offer a compelling advantage. At 21.5 by 60 millimeters, it was awkwardly sized for most consumer electronics. AA batteries were compact enough for small devices, C and D cells packed enough energy for flashlights and boomboxes, and the 9-volt battery handled smoke detectors and guitar pedals. There was no popular product category where a B battery was the best fit, so retailers stopped stocking them and manufacturers stopped designing around them.
Other “Missing” Battery Sizes
B isn’t the only gap on the shelf. The single A battery also exists as a standardized size but is rarely sold on its own. You’ve probably never bought one, yet A cells are sometimes bundled inside multi-cell battery packs, like those used in older laptop batteries or specialty equipment. The same is true for several other ANSI-designated sizes that have valid specifications but no mainstream consumer demand.
Battery survival is driven entirely by market feedback. If enough devices use a particular size, factories keep producing it, stores keep carrying it, and prices stay low. That cycle reinforces itself: designers choose sizes that are cheap and widely available, which keeps those sizes cheap and widely available. Sizes without a critical mass of demand, like B, get quietly dropped from production lines and retail inventory. The standard still recognizes them, but no one is making them in bulk.
Can You Still Buy a B Battery?
Specialty electronics suppliers occasionally stock B-size cells for hobbyists restoring vintage radios or maintaining legacy equipment. They’re not something you’ll find at a hardware store or pharmacy. If you’re working on an antique vacuum tube radio and need plate voltage, modern builders typically use power supplies or battery eliminators rather than hunting down original B batteries. The designation lives on in technical documents, but for everyday purposes, the B battery is a relic of a time when radio listeners needed three separate batteries just to hear the evening news.