What Is the Difference Between NiMH Batteries & NiCd Batteries?

Written by c.a. rubino
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What Is the Difference Between NiMH Batteries & NiCd Batteries?
Both NiMH and NiCd batteries come in several different forms, like AA. (Jupiterimages/Polka Dot/Getty Images)

The conveniences of modern technology and the digital information age are all around. Digital cameras, cell phones, laptops, MP3 players and PDA devices are just a small selection of devices that you can carry with you to keep connected to the rest of the digital world. All these devices need power in order to run. NiMH and NiCd are two types of rechargeable batteries that you can find in many portable devices.


NiCd stands for "nickel cadmium," which first appeared in the early 1900s. Up until the early 2000s, NiCd batteries have dominated the rechargeable battery market, having higher capacity and life than lead or alkaline rechargeable batteries. NiMH is a relatively new technology and stands for "nickel metal hydride." NiMH was invented in 1989 from research involving nickel-hydrogen batteries, which are used on satellites. As the cost of producing NiMH batteries has decreased, they have quickly overtaken NiCd batteries in popularity.


When it comes to the amount of energy that is able to be stored in the battery, NiMH has the clear advantage over NiCd batteries. NiMH is able to store more than twice the amount of energy as NiCd batteries. This means that NiMH-powered devices will enjoy much longer operating time on battery power than those using NiCd batteries.


The actual power produced by NiMH and NiCd batteries is identical. Both the batteries are able to produce the same levels of energy. This means that both batteries would be able to power the same types of devices. This is the one category where NiCd is not inferior to NiMH batteries.


Another major advantage of NiMH batteries is that they don't use cadmium, one of the key components of NiCd batteries. Cadmium is a metal found on the earth's crust and is usually associated with zinc, lead and copper. Cadmium is a toxic substance that has environmental and health concerns when not disposed of properly. NiMH technology does not contain cadmium and as a result is more environmentally friendly.


One of the other major differences between NiMH and NiCd batteries is the memory effect. When an NiCd battery is recharged before it is fully discharged, then under some specific conditions the battery may remember at what capacity the recharge began. When the battery then reaches that same capacity, the energy level will drop, effectively acting as though the battery were fully discharged. In theory this means that NiCd batteries need to be fully discharged before they can be charged again. While this memory effect is rare and should only happen under laboratory conditions, NiMH batteries have shown no memory effect; they can be recharged at any time and will never develop any form of memory.

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