[Elecraft] 4V 450mAH AA Lithium batteries [KX1]

[David A.Belsley]

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