Re: recharing and batteries

[buffingt@chaph.usc.edu (Roger J. Buffington)]

On Sat, 9 Sep 95 12:38:37 -0400 you wrote:

>">Roger, do you have measurements that show this is the case, or are you
>guessing from what you think you know?
>
>I have tried to measure this effect, and have been unable to do so ...

Actually, I base my comment on 3 things:
1)	About a year ago, several people here on the list reported that
they had more or less ruined batteries from keeping them plugged into
the AC charger on a continuous basis for a long time.  Therefore, they
did, in effect "measure" this.

2)	There is a fair amount of technical literature (I'm a radio ham,
and therefore I waste my time reading such stuff)  that indicates
keeping a battery charged such that it stays warm all the time
accelerates the chemical reactions inside the battery that cause it to
age.  This shortens battery life.  How good/bad the Thinkpad batteries
are in particular in this regards I couldn't say.  If the experiences
noted in 1) are accurate, however, well....

3)	Please note that my comments had NOTHING to do with the so-called
"memory effect" which allegedly causes batteries that are not fully
re-charged  to "plateau" at a charging level that is less than the
rated, optimal level.  For example, supposedly a battery that was
frequently recharged to only 80% of a full charge, from perhaps being
only 50% discharged, will eventually only be able to hold around an
80% charge, due to the "memory effect."
	In actual fact, the memory effect originated in space satellite
applications, where orbiting satellites re-charged their batteries
once per orbit, very very regularly, as they moved from shade to
sunlight.  This "memory effect" had the effect of degrading their
batteries, which of course was very expensive since the batteries
couldn't be replaced.  However, I have read literature from
knowledgeable sources that contends that this phenomenon is very rare,
and is in fact very difficult to duplicate experimentally in testing
laboratories.  For practical purposes, it is something folks like us
can ignore, so it is said.

	The memory effect is a different thing than degradation caused by
constant charging/recharging.  Batteries degrade over time by being
charged, partly due to chemical reactions caused by the charging
process.  Feel your battery after being plugged into the charger.  It
is warm.  Batteries have a finite number of charges per battery life. 
This fact, combined with reports of real-world degradation by Thinkpad
users on this list, is what I based my comments on.

	I have not, incidentally, experienced the phenomenon myself. 
However, I've been careful not to abuse my batteries by constantly
charging them.  Law school is expensive, and I don't need any $200
battery replacement hits.

Hope this answered your question about what my comments were based
upon.
Roger J. Buffington
AB6WR
USC Law, Class of '97
Go Trojans!
WARPing with PM-Mail

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