The nickel-cadmium battery (commonly abbreviated NiCd or NiCad) is a popular type of rechargeable battery for electric-powered R/C models as well as portable electronics and toys. Active chemicals are nickel (Ni) and cadmium (Cd). In general, NiCd batteries have a lower capacity than nickel metal hydride (NiMH), alkaline or carbon-zinc batteries of the same size. For example, an alkaline or carbon-zinc AA battery is rated at 1.5 volts while an AA NiCd is rated at only 1.2 volts, making it somwhat underpowered for use as a primary battery in some appliactions. However, they are generally more robust and less sensitive to abuse and overcharging than NiMH batteries, and therefore don't require a peak charger.
In 1899, Waldemar Jungner of Sweden created the first nickel-cadmium battery. At this time, the only direct competitor was the lead acid battery. The nickel-cadmium battery offered several advantages in certain applications. Even early nickel-cadmium batteries were physically and chemically robust. With minor improvements to the first prototypes, energy density rapidly increased to about half of that of primary batteries, significantly better than lead acid batteries.
In 1910, a company was formed to produce industrial nickel-cadmium batteries in Sweden. The first production in the United States began in 1946.
Nickel-cadmium batteries and R/C battery packs have the unusual trait of developing a "memory" through frequent charge and discharge cycles. When this happens, the battery cannot be charged to its full capacity. To prevent this, the R/C pack should be completely discharged with the aid of an automotive lamp before attempting to recharge it. By comparison, nickel metal hydride and lithium polymer batteries should never be discharged in this manner.