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From: dbell@cup.portal.com (David J Bell)
Newsgroups: sci.electronics
Subject: Re: rechargable battery "memory"
Message-ID: <32645@cup.portal.com>
Date: 10 Aug 90 04:19:19 GMT
References: <105@javelina.cs.arizona.edu>
  <1990Aug9.223441.19242@hayes.fai.alaska.edu>
Distribution: na
Organization: The Portal System (TM)
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>>With the plethora of cordless, rechargable appliances and tools in our
>>machine room tool cabinet, the question of the which charging schedule 
>>will prolong the life of the batteries and provide a reasonable useful
>>charge has come up.  The best information we have is that the batteries
>>should not be recharged until they have been drained to avoid giving
>>them a memory (e.g., if a fully-charged flashlight is consistently used
>>for 5 minutes, and then recharged, it will soon develop a memory, and will
>>only shine for 5 minutes before it is discharged).

>     There was an article in "Power Electronics" magazine a couple of years ag
o
>about this very topic.  The consensus of the manufacturers was that there ain'
t
>no such thing, or least they can't duplicate it under lab conditions.

BZZZZTT!    Wrong.... I don't know where they got that idea, that
NiCd cells don;t develop "charge memory". It doesn't occur to the
extent suggested in the first posting (5 minute life, eventually)
unless a cell has been ruined, but NiCds, and most other secondary
cells need to be reconditioned once in a while. I am an engineer in
a spacecraft power systems division of a large aerospace firm; there
is a marked improvement in "old" cells after they have been fully
discharged, then shorted down with ~1 ohm resistor for 12-24 hours.
The available capacity increases 50-100% in some cases...

There is a more serious problem, when discharging exhausted cells:
there is a possibility of one (weaker) cell being reversed, that
is - discharged through zero, by the rest of the cells discharging
through the load. This is usually what ruins a rechargeable pack...

Dave        dbell@cup.portal.com