Miniature Power

The miniaturization of the battery began in war. Image courtesy Eric S. Hintz.

A small, hidden force in our world keeps hearts beating and clocks ticking. Miniature batteries, or “button cells,” inconspicuously power our watches, hearing aids, and pacemakers. Meanwhile, standard alkaline batteries—slightly larger and even more pervasive in the familiar AA, AAA, and 9-volt sizes—run our flash cameras, portable radios, flashlights, and smoke detectors. We rarely see the batteries when they’re hard at work, powering much of our modern technological society. It’s easy to forget they started out big.

The first batteries may date to as early as the 2nd century BCE, based on a 1936 find in Baghdad, Iraq. Workers there unearthed a strange-looking artifact: a sealed clay vase with a protruding iron rod surrounded by a cylindrical copper tube. When archaeologists constructed a replica and filled the vase with an acidlike vinegar or grape juice, the proto-battery produced two volts of potential. The archaeologists speculated that the early battery had been used for electroplating gold onto jewelry or as an early version of (mild) shock therapy.

All batteries feature three essential elements: a negative terminal (anode), a positive terminal (cathode), and a medium separating them (electrolyte). When put to work, the internal chemical reaction begins: the anode loses negative ions and gains positive ones, while the cathode works in reverse. These ions move through the electrolyte, with the negative ones collected along a metal rod as usable electrical current. In 1801 Alessandro Volta demonstrated the first modern battery—a large “pile” of alternating silver and zinc disks separated by an electrolyte of brine-soaked cloth—for Napoleon Bonaparte. Since then, inventors from Georges Leclanché to Thomas Edison have created new battery designs by carefully selecting different chemical combinations, resulting in zinc-carbon, nickel-cadmium, and lead-acid cells.

Before the rise of the modern electric-power grid and plug-in appliances, batteries powered all things electrical—from radios to doorbells to early flashlights. But they remained bulky until World War II, an event that created an insatiable demand for portable batteries to power the wireless radios and mine detectors used by U.S. and Allied forces. The zinc-carbon battery packs commonly used in army radios during the early 1940s were large and heavy by today’s standards—a square 1.3-inch block nearly a foot in length. Worse, these batteries were unsealed and thus vulnerable to temperature and humidity effects that corroded terminals and caused spontaneous discharging during storage, resulting in a short, five-hour service life. A soldier carrying a portable walkie-talkie found his effective radio range decreasing as the battery’s voltage declined. Soldiers also complained about constantly replacing batteries and of often finding the replacement cells unusable.

To solve these problems, the U.S. Army’s Signal Corps turned to the National Inventors Council, a wartime agency established in 1940 to mobilize American citizen-inventors to “Invent for Victory!” The NIC referred the battery problem to Samuel Ruben (1900-1988), an independent inventor from New York City. In 1942-1943 Ruben developed a zinc-mercuric oxide battery with a 25-hour service life and a sealed, airtight casing that resisted the effects of heat and humidity. The original prototype cell was a small, lightweight cylinder: only 0.533 inches long and 0.610 inches in diameter, weighing 0.25 ounces. Although long-lasting, a single cell could not provide enough voltage to power an army radio; so the Signal Corps combined 72 cells in series within a larger battery pack. The P. R. Mallory Company of Indianapolis manufactured the batteries and by war’s end was producing over one million cells per day.

After the war Ruben and Mallory adapted the cells for peacetime applications like hearing aids, watches, and pacemakers, placing miniature batteries at the vanguard of the postwar miniaturization movement alongside the better-known transistor. Mallory’s mercury batteries helped miniaturize vacuum-tube hearing aids starting in 1946, two years before the invention of the transistor and six years before the appearance of the first transistor-based hearing aids. Mallory’s miniature cells also powered the Bulova Accutron, the first transistor-based electric watch, introduced in 1960. That same year 10 Mallory cells powered the first successful cardiac pacemaker implanted in a human being. Meanwhile, NASA and the military continued to employ Mallory’s miniature mercury batteries in all kinds of applications, including communications satellites, missile-guidance systems, air-sea rescue beacons for downed pilots, personal radiation-detection devices, and sea-based sonobuoys that tracked ship and submarine movements.

Within a decade relentless innovation signaled the mercury battery’s eventual demise. As early as 1949 engineers at Ray-O-Vac and Union Carbide began experimenting with new cell systems based on Ruben’s design, while looking for less expensive materials. By substituting cheaper manganese dioxide for Ruben’s mercuric-oxide cathode, the new cells maintained the mercury’s high performance at a much lower cost; the resulting “alkalines” have remained the most popular consumer batteries ever since. Mallory, working again with Ruben, introduced its own line of alkaline cells in 1961, both in miniature configurations and the standard AA, AAA, C, and D sizes. As sales soared, the P. R. Mallory Company rebranded in 1965, becoming the multibillion-dollar company we know today as Duracell.

Throughout the 1970s and 1980s Duracell and its competitors introduced new cell systems that, alongside the alkalines, continued to crowd out the mercury-based batteries. High-powered silver-oxide cells became the preferred replacement battery for hearing aids, watches, and calculators; super-long-lasting lithium-iodine batteries supplanted mercury cells in pacemakers. Environmental concerns also hastened the mercury battery’s demise; the cell’s chemical reaction produced toxic elemental mercury as a by-product, and watchdogs warned that discarded cells might contaminate local water tables or pollute the atmosphere if incinerated. Eventually, Congress’s “Mercury-Containing and Rechargeable Battery Management Act” of 1996 outlawed the sale of mercury cells in the United States.

Despite the eclipse of mercury batteries, the general construction principles of Ruben’s wartime design—an alkaline electrolyte, precise anode-cathode proportions, and a hermetically sealed canister—set the standard for all the alkalines that followed. So when your watch dies and brings the hidden, quotidian button battery into plain sight, you might pause to remember how the urgency of war inspired an inventor named Samuel Ruben to shrink your batteries.

Eric S. Hintz is a historian with the Lemelson Center for the Study of Invention and Innovation at the Smithsonian’s National Museum of American History.

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