Path: utzoo!mnetor!uunet!husc6!mit-eddie!ll-xn!ames!umd5!mimsy!oddjob!gargoyle!ihnp4!cbosgd!clyde!watmath!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: sci.electronics
Subject: Re: Rejuvinating Rechargeable Batteries
Message-ID: <15529@onfcanim.UUCP>
Date: 7 Jan 88 04:24:18 GMT
References: <2428@emory.uucp> <897@neoucom.UUCP>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Organization: National Film Board / Office national du film, Montreal
Lines: 27

In article <897@neoucom.UUCP> wtm@neoucom.UUCP (Bill Mayhew) writes:
>
>Genrally, running a battery down to empy is a good thing in the
>case of NiCd cells, as it ensures that all cells are fully depleted
>and thus all cells will take a full charge.  This, of course,
>doesn't mean leaving it on for days.

More precisely, it is a *good* thing to use the battery-powered device
until its low-battery warning comes on, at least once or twice a month.
As Bill notes, this prevents NiCd cell "memory effect".

However, it is a very *bad* thing to leave the power switch on beyond the
low-battery warning point, particularly after the device stops functioning.
Since the actual capacity of each cell in the battery pack differs, one
of them will eventually reach zero charge while the others still have
some remaining charge.  At this point, if current is still flowing, the
discharged cell begins charging in *reverse* - a good way to destroy it
rapidly.

If you want to completely discharge each cell in the pack, you have to
discharge each cell individually (through a resistor) - just connecting
a resistor across the pack as a whole will probably reverse-charge one
or more cells.

Yours for longer nicad life,

	Dave Martindale