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From: darrelj@sm.unisys.com (Darrel VanBuer)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Overcharging NiCad batteries?
Keywords: NiCad rechargeable batteries, laptops
Message-ID: 
Date: 26 Sep 88 15:29:41 GMT
References: <3008@dalcs.UUCP> <14705@agate.BERKELEY.EDU>
Reply-To: darrelj@sm.unisys.com (Darrel VanBuer)
Distribution: na
Organization: Unisys Santa Monica
Lines: 12

I use NiCds as a ham, but characteristics are general.
On charging: once the battery is fully charged, the extra current goes
into heating up the battery and disassociating water into hydrogen and
oxygen.  Both of these are hard on the battery.
On discharging: NiCds eventually "learn" how you use them.  If you use
25% and recharge regularly, they eventually will give out after 25%
use.  While its not necessary to go all the way down every time, you
should do so regularly.  BUT don't over discharge either, because if
you go beyond the capacity of the weakest cell in the battery, it gets
run in reverse which causes whiskers of metal to grow and eventually
short out the cell.  Also with a partial discharge, its hard to guess
how long to charge without overcharging.