Nicad FAQ

The NiCd and NiMH Story or The Care and Feeding of Batteries

Parts of the pages forming this section are very loosely based upon the "NiCd FAQ" originally posted by Dave Bushong, OPEN/image Recognition Products and written by Ken A. Nishimura (KO6AF) (Titled "Some Ramblings About NiCd Batteries Ken A. Nishimura (KO6AF)". It was acquired some time last year from a source long forgotten. However it is one of the better and fuller descriptions of the chemistry and characteristics of both NiCad and NiMH batteries. It concentrates more on NiCd than NiMH, however despite the markedly different chemistry the characteristics of the two types of battery are similar in many respects. The disclaimer was attached to the original post and applies to all sections of this article.

Any corrections or additions would be most welcome and should be sent to:- webmaster@wppltd.demon.co.uk

Index

Pictures of the insides of some Phone Batteries

The Chemistry of NiCd, NiMH and Lithium batteries

The Memory Effect

Charging Phone Batteries

Charging methods in general

Life Cycle - or why batteries eventually die.

Summary:

Charge control is the key to battery management.

More batteries are destroyed or damaged by bad charging techniques than all other causes combined. Once a battery reaches full charge, the charging current has to go somewhere — most often, generating heat and gases. Both are bad for batteries.

Heat is the enemy of batteries.

A battery stored, used, or charged under high temperature conditions will die an early death. Heat causes the separator to weaken, the seals to weaken, and greatly accelerates changes in the plate material, some of which cause the dreaded memory effect . So even though the cells may not vent, the heat by-product is wearing down the cells. Specifically, hydrolysis or degradation of the separator material, usually polyamide, is greatly accelerated at high temperatures. This leads to premature cell failure .

DON'T deliberately discharge the batteries to avoid memory.

DO let the cells discharge to 1.0V/cell on occasion through normal use.

DON'T leave the cells on trickle charge for long times, unless voltage depression can be tolerated.

DO protect the cells from high temperature both in charging and storage.

DON'T overcharge the cells. Use a good charging technique.

DO choose cells wisely. Sponge/foam plates will not tolerate high charge/discharge currents as well as sintered plate.

What if I want to learn even more about NiCd and other batteries?

There are several good texts on batteries. One is quite new and contains fairly contemporary material:

Maintenance-Free Batteries by D. Berndt, Research Studies Press, Ltd., Taunton, Somerset, England in conjunction with J. Wiley & Sons, New York, 1993. ISBN 0-86380-143-9.

A quite good technical description of battery technology in general (but not a lot on NiMH) can be found here.

Note: Panasonic, Sanyo, and Millenium are registered trademarks ® of their respective holders. This document is not intended to promote a particular manufacturer or product. Material contain herein is believed to be correct, but the author cannot be held responsible for error, either editorial or material contained within. Use of the information above is at the sole risk of the reader. Permission granted to use any of the material above, provided this disclaimer is preserved in its entirety.

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