What is the difference between nickel metal hydride and nickel cadmium rechargeable batteries?

Nickel cadmium came out first. Nickel-metal hydrides are replacing them, because they don't suffer from the memory effect. More.

Both NiCad and NiMH batteries are rechargeable. The main difference between the two is the fact that NIMH batteries offer higher energy densities than NiCads. In other words, pound for pound, NIMH delivers approximately 30% more capacity than its NiCad counterpart.

What this translates into is increased runtime from the battery with no additional bulk. NIMH also offers another major advantage: NiCad batteries tend to suffer from what is called a "memory effect". What this means is that when a NiCad battery is only partially discharged before charging, the battery "forgets" that it has the capacity to further discharge all the way down.

To illustrate: If you, on a regular basis, fully charge your battery and then use only 40% of its capacity before the next recharge, eventually the battery will become unaware of its extra 60% capacity which had remained unused. Your battery will remain functional, but only at 40% of its original capacity. The way to avoid the dreaded "memory effect" ... more.

NiMH batteries generally provide at least 30% more talk time than NiCd batteries and take approximately 20% longer to charge. NiMH batteries are also considered more "environmentally friendly" than NiCd batteries and are not susceptible to memory effect. (Memory Effect refers to a NiCd battery's inability to be charged to full capacity over time.

Firstly there is no difference in the voltage of the cells; they both produce 1.2 volts per cell. NiCd batteries have less capacity but around three times more cycle life than NiMH Batteries. NiCd batteries are more suitable for high drain and fast charge appliances such as Cordless Power Tools and appliances running motors.

Large capacity NiCds are still in use for Aviation, Solar Storage appliances, Emergency Generator Set Start and Theatre Lighting. The reputation of NiCds in these applications is one of reliability and longevity. NiMH batteries have a higher capacity to size ratio but only have around one third of the cycle life of a NiCd battery.

If a NiMH battery is treated like a NiCd and deep discharged regularly it will not have a long lifespan. NiMH batteries are not known for having the 'memory effect' problems of NiCds. They are very suitable where higher capacity is required in appliances such as Mobile Cellular phones, Laptop Computers, Video Cameras and Hand Held ... more.

Nickel-Metal Hydride (Ni-MH) batteries provide up to 200% more power than Nickel Cadmium (Ni-CD) rechargeable batteries, will significantly outperform alkaline batteries, in most digital applications and will greatly outperform Ni-CD batteries in high-drain applications. Ni-MH batteries have a rechargeable life of up to 1000 cycles, 25% more than Ni-CD. Ni-MH batteries have no Cadmium added.

Cadmium is hazardous to the environment. More.

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