The nickel-cadmium battery (commonly abbreviated NiCd and pronounced NYE-kad) is a type of rechargeable battery work by oxidizing nickelic hydroxide into nickelous hydroxide and metallic cadmium as electrodes which produces two free electrones for every transaction. 
 

The abbreviation NiCad is a registered trademark of SAFT Corporation and should not be used to refer generically to nickel-cadmium batteries, although this brand name is commonly used to describe all nickel-cadmium batteries. On the other hand, the abbreviation NiCd is derived from the chemical symbols of nickel (Ni) and cadmium (Cd), though it is not to be confused with a chemical formula.

Nickel Cadmium batteries were the first rechargable batteries to be widely commercially available, and they are commonly utilized in power tools.

There are two types of NiCd batteries: sealed and vented.

Sealed NiCd cells may be used individually, or assembled into battery packs containing two or more cells. Small NiCd dry cells are used for portable electronics and toys, often using cells manufactured in the same sizes as primary cells. When NiCds are substituted for primary cells, the lower terminal voltage and smaller amperehour capacity may reduce performance as compared to primary cells.

Specialty NiCd batteries have a niche market in the area of cordless and wireless telephones, emergency lighting, model airplanes, as well as power tools.

With a relatively low internal resistance, a NiCd battery can supply high surge currents. This makes them a favourable choice for remote-controlled electric model airplanes, boats, and cars, as well as cordless power tools and camera flash units. Larger flooded cells are used for aircraft starting batteries, electric vehicles, and standby power.

Nickel-cadmium cells have a nominal cell potential of 1.2 V. This is lower than the 1.5 V of many popular primary cells, and consequently they are not appropriate as a replacement in all applications.

NiCd batteries used to replace 9 V batteries usually only have six cells, for a terminal voltage of 7.2 volts. While most pocket radios will operate satisfactorily at this voltage, some manufacturers made 8.4 volt batteries with seven cells for more critical applications.

12 V NiCd batteries are made up of 10 cells connected in series.

Advances in battery-manufacturing technologies throughout the second half of the twentieth century have made batteries increasingly cheaper to produce. Battery-powered devices in general have increased in popularity. As of 2000, about 1.5 billion NiCd batteries were produced annually. While Ni-Cd never became widely used as a replacement for lead-acid batteries in the areas where those batteries dominate, up until the mid 1990s, Ni-Cds had an overwhelming majority of the market share for rechargeable batteries in consumer electronics.

Even with full drainage (called deep discharging), all batteries have a limit to the number of times they can be recharged. The maximum for most NiCad batteries is about one thousand recharges.

Pros:

• Inexpensive
• High number of recharges possible
• Fast recharging
• Fast and simple charge, even after prolonged storage.
   
• High number of charge/discharge cycles - if properly maintained, nickel-cadmium provides over 1000 charge/discharge cycles.
   
• Good load performance - nickel-cadmium allows recharging at low temperatures.
   
• Long shelf life - five year storage is possible. Some priming prior to use will be required.
   
• Simple storage and transportation - most airfreight companies accept nickel-cadmium without special conditions.
   
• Good low temperature performance.
   
• Forgiving if abused - nickel-cadmium is one of the most rugged rechargeable batteries.
   
• Economically priced - nickel-cadmium is lowest in terms of cost per cycle.
   
• Available in a wide range of sizes and performance options - most nickel-cadmium cells are cylindrical.

Cons:

• Low charge capacity
• Cadmium is toxic and should be recycled properly
• Memory effect problems
   

• Relatively low energy density.
   
• Memory effect - nickel-cadmium must periodically be exercised (discharge/charge).
   
• Environmentally unfriendly - nickel-cadmium contains toxic metals. Some countries restrict its use.
   
• Relatively high self-discharge - needs recharging after storage
   

Alternatives to Nickel Cadmium batteries include:

• Nickel-Metal Hydride
• Lithium Ion
• Lithium Polymer

Although Nickel-Metal Hydride and Lithium Ion batteries are becoming more popular in mobile computers, Ni-Cd batteries are still the most widely sold.