Mercury battery

The mercury battery emerged from a wartime crisis that revealed the limitations of existing power sources. In 1942, the U.S. Army Signal Corps approached Samuel Ruben with an urgent problem: standard zinc-carbon batteries failed catastrophically in the Pacific theater's heat and humidity just when new portable electronics—walkie-talkies, metal detectors, proximity fuses—demanded reliable compact power. Ruben, an independent inventor and electrochemist, knew that zinc-mercuric oxide chemistry had been understood since the 1800s but remained impractical. His contribution was engineering the reaction into a stable, miniature form.

The mercury battery solved four problems simultaneously. It maintained a constant 1.35 volts within 1% variance until the final 5% of discharge—unlike zinc-carbon batteries, whose voltage dropped steadily, causing radios to fade. It stored for up to ten years without degradation. It performed reliably in extreme temperatures and humidity. And it packed high energy density into the button cell format that military equipment required.

Ruben licensed the technology to P.R. Mallory & Co. in 1944. By 1947, the first consumer application appeared: mercury button cells for hearing aids, enabling single in-ear devices that replaced bulky battery packs. Electric watches adopted the technology for its flat voltage curve—essential for accurate timekeeping. Cameras relied on mercury cells for light meters. By 1964, Mallory had registered the "Duracell" trademark (portmanteau of "durable cell"), building a consumer brand on the foundation of Ruben's wartime invention.

The cascade carried a price. Mercury is a neurotoxin that bioaccumulates in food webs. Decades of disposal contaminated groundwater and released vapor when batteries were incinerated. On May 13, 1996, the United States passed the Mercury-Containing and Rechargeable Battery Management Act, banning mercury in most batteries. The international Minamata Convention later required global phaseout. Zinc-air, silver oxide, and lithium chemistries now fill the niches mercury batteries created—but for fifty years, Samuel Ruben's wartime solution powered the miniaturized electronics that defined postwar consumer culture.