Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!ucbcad!ucbvax!cbosgd!mandrill!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: sci.electronics
Subject: Re: Rejuvinating Rechargeable Batteries
Message-ID: <897@neoucom.UUCP>
Date: 29 Dec 87 13:21:17 GMT
References: <2428@emory.uucp>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 39
Summary: Fixing NiCd batteries


<<bad battery pack on a Sony D7>>

I'm not sure about the D7, but the hard case for the D5 used a
battery pack that was identical to one of the camcorders that Sony
makes, but the battery is kind of expensive.  One might be able to
obtain an equivalent battery from 47th St. photo or a similar
source, though.  Also Spiratone has many such A/V accessories.

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.

If a NiCd cell is completely discharged, it will short out thus
rendering it potentially useless.

Over charging a NiCd battery is bad for it because the heat
build-up can kill the cells.

Only partially discharging a NiCd battery can cause some cells to
become more depleted than others in the battery, due to normal
statistical variation of the real world.  Subsequent partial use
and recharges causes the bad cell to get more out of sync, until it
is fully depleted and shorts out.

Sometimes a shorted cell can be rejuvenated by charging up a 40,000
uF or so capacitor to around 20 volts, removing said cap from power
supply and applying it + to +, - to - on the shorted cell.
Sometimes, you'll get lucky and break the short.  Often several
current pulses need be applied to clear the short.  Such
rejuvenated cells are seldom as good as fresh cell, but the
technique is useful to get a piece of gear back on line quickly
when a replacement cell is not available.

The Sony battery packs are usually pretty well sealed, so you'd
have to do some work with an X-acto knife to get at the individual
cell of the battery.

--Bill