The 'Expert' at "DC Solutions" told me that LiI cells do not like deep
discharge, and that I should expect around 200 full cycles from them compared
to 800+ for NiCad.

This has been confirmed by a notation in the Nokia Cell phone that says
'charge every night for maximum battery life', and my own experience with
LiI cells that last about a year or so before there is a noticeable loss
in capacity (standby time in an unchanging load environment).

This faq has a detailed explanation of why we see a 'memory effect'
in Nicads.
http://vancouver-webpages.com/peter/nicad.faq

"The more common "memory effect" isn't memory at all, but voltage
depression caused by overcharging.  Positive plate electrochemistry
is very complicated, but overcharging changes the crystal structure
of the nickelic hydroxide from beta-Nickelic Hydroxide to gamma-Nickelic
hydroxide.  The electrochemical potential of the gamma form is
about 40 to 50 mV less than the beta form.  This results in
a lower discharge voltage.  In a six cell (7.2v) pack, this means
a loss of 300 mV.  Trick?  Don't overcharge.  Leaving cells on a
trickle charger encourages formation of gamma nickelic hydroxide.
Expect the cells to discharge at a lower voltage."


It has more to do with poor charging practice than with true 'memory
(as found in batteries used in satellites to power them when eclipsed
by the earth).

"In fact, 'memory' is always a completely reversible
condition; even in those rare cases where 'memory' cannot be avoided, it
can easily be erased.  Unfortunately, the idea of memory-related loss of
capacity has been with us since.  Realistically, however, ' memory' CANNOT
exist if ANY ONE of the following conditions holds:                 ^^^^^^
         ^^^ ^^^
        A. Batteries achieve full overcharge.
        B. Discharge is not exactly the same each cycle - plus or minus 2-3%
        C. Discharge is to less than 1.0 volt per cell."


The problem is that individual cells
have unique capacities and are not always fully charged when in a 'battery'
of cells. I have found that supposedly 'bad' packs work just fine when charged
at a low rate (1/50C) for a week. The low rate charge 'tops up' the cells
weakened by the reverse charging that happens when the weak cell is exhausted,
but the higher capacity cells keep pushing current through it. This is contrary
to the FAQ, but it worked for my Makita battery packs.

Of course YMMV.

Robert

Herbert Graf wrote:
>
> Just wondering, what is the collective opinion on how to treat lithium ion batteries? I just purchased a Dell Axim  handheld computer (very sweet) and it comes with a lithium ion battery. I hope to get the longest service life out of it. Should I keep them topped up or should I run them down each time before charging? Should I just keep it topped up? What is worse, number of charging cycles, or the length of each cycle? Thanks for your opinions and insights. TTYL

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