A NiCd battery is a battery which uses nickel and cadmium as its electrodes. It is generally pronounced nigh-cad, although many people also simply say nickel cadmium. It is important to note that although Ni and Cd are chemical symbols for the pure elements, a NiCd battery actually uses nickel oxide hydroxide and metallic cadmium in its operation. The NiCd battery is one of the most commonly-used types of rechargeable battery, and is seen widely in consumer applications.
Most primary cells used in batteries have a nominal potential of 1.5V, which is higher than that of a NiCd battery, which is 1.2V. However, most primary cells also have a variable voltage, which reduces as the battery expends its charge. In most batteries this can get as low as 0.9V, whereas a NiCd battery loses very little cell potential as it runs down, so that even as it approaches a complete loss of charge it is still generating around 1.2V. As a result, most devices intended to run on batteries can use NiCd batteries, even with their lower nominal potential.
Although many people have only become aware of the NiCd battery in recent years, it was first produced in 1899 in Sweden. In the United States, Thomas Edison produced nickel-iron batteries not long after, but it wasn’t until the mid-1940s that the NiCd battery began being produced in the United States. Because of higher costs, however, lead-acid batteries remained the dominant battery type in the United States well into the 1990s.
Beginning in the 1980s, the rechargeable NiCd battery began to become more popular as rechargeable batteries in general found increased popularity. Throughout the 1980s and early-1990s, NiCd batteries continued to dominate the rechargeable market, when both lithium ion and nickel-metal hydride (NiMH) batteries began to grow in market share. In recent years, nickel-metal hydride has overwhelmed the popularity of NiCd batteries, which are not seen nearly as often as they once were.
Although in the 1990s lithium ion batteries began to find a large market in custom rechargeable batteries for things like laptops, NiCd batteries remained popular. This was largely due to the difference in how the two battery types handle a complete loss of charge. While a lithium ion battery can essentially not handle losing its charge completely, a NiCd battery can be discharged completely for long-term storage and still be recharged in perfect health. NiCd batteries are also able to cycle more than most other battery types, and can recharge more quickly than many other battery types.
Nickel-metal hydride batteries are the primary competitor to the NiCd battery, and have largely rendered them obsolete in many areas. A NiMH battery is cheaper, less toxic, and generally has a higher capacity than a comparable NiCd battery, making it the better choice for many applications. One of the only advantages NiCd batteries have over NiMH is that their self-discharge rate is much lower, so for applications where the batteries need to last for long periods of time and a low amount of active draw is being used, NiCd batteries can be preferable. For example, television remotes, which use very little active electricity, often use NiCd batteries instead of NiMH batteries, which would passively run down more quickly.