On Mar 21, 2005, at 4:27 PM, Don wrote:
About rechargable lithium batteries in general ....
Many folks do not know this and I had to find it out the hard way when
I bought some rechargable lithium batteries for my camera.
Rechargable (Lithium ion) batteries decline in quality with age. It
does not matter how much they are used. Beginning when they are
manufactured they gradually develop an increase in internal impedance
until eventually the terminal voltage under load falls to an unusable
level. This may not be serious for applications that do not pull high
peak current. It is important, though, if you are really drawing a
fair ammount of current (at the one hour rate, for instance). You can
quickly 'google' quite a bit of information on this.
It is my understanding that this crystaline layer forms most rapidly
when the Li batteries are kept fully charged for a long time (or kept
on the charger for prolonged periods). I've read a figure that they
store best at about 40% charge. The report I read (I, unfortunately,
did not keep the URL) also indicated that the layer can be broken up
with a deep (but by no means complete) discharge and full recharging.
The batteries are apparently not really dead, but the high internal
resistance causes the effective voltage to be sufficiently low to cause
the camera's low-battery voltage sensor to think the battery is
drained. If you still have your "dead" Li-Ion batteries, you might try
giving them a good discharge across, say, a 10 ohm, 10w resistor.
Monitor the voltage with a meter, and stop the process when the voltage
starts dropping noticeably while you watch. You'll likely notice at
the start that the voltage remains fairly constant, dropping only very,
very slowly, indicating that the "dead" battery does indeed still have
a charge.
It was these notions that prompted me to post a question to this
reflector the other day: specifically, which is better for Li-Ion
batteries, to be kept on the charger so as to reduce the number of
charge/discharge cycles or to be allowed to charge and discharge so as
to reduce the problems that arise when the battery is "stored" at full
charge? The two actions appear to be in conflict.
I got no answer. I would surely like to hear from any of those out
there who really know about Li-Ion batteries. There appears to be a
lot of misinformation about them on the web (I hope I haven't added to
it with the above), much of which seems to arise over confusions of
old-wives'-tales borrowed from Ni-Cd and Nimh batteries. I think it is
going to take years for a proper set of facts about Li batteries to
emerge and become established.
best wishes,
dave belsley, w1euy
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