I think it is definitely worth it to take a look at Li-Poly cells. You can
buy them from http://www.fmadirect.com which offers the Kokam cells or
http://www.b-p-p.com which offers both Kokam and E-Tec. Kokam has just come
out with some very high drain rate cells (10C), but for laptop use, even
the lower drain ones should be fine. They have about three times the energy
density per mass (and, guessing from looking at them, about a factor of 2
by volume) better than NiMH. In the few tests that I've done so far, I've
also found them to be more consistent than NiMH. This is in the sense that,
from charge to charge, they seem to deliver a more consistent total amount
of energy to the same cutoff voltage.

I found NiMH harder to charge (having to use delta-peak type charge
detection versus the simpler constant voltage-constant current sequence of
the Li-Poly). In order to get a consistent output, I often had to trickle
charge the packs in order to equalize the cells (this may have been related
to the high drain rates that I was using, about 7C). Even so, the end of
the pack's useful charge was often dictated by only one of the cells, while
there was still useful energy in the remaining cells. I have so far found
Li-Poly to have none of these problems.

Finally, Li-Poly cells can be easily paralleled, whereas that is (I have
heard) much more difficult to do safely and effectively for NiMH.

Sean

At 06:16 PM 4/27/2003 -0500, you wrote:
>I've never really tried to stretch the battery life, it does pretty good
>as is.
>
>Gell Batteries are relatively easy to deal with, and if you look, you'll
>find 4V units so you can stack up 16V easily. However, they certainly
>don't have as much watts per bulk or pound, as NIMH.  If I were you, I
>would look at some NIMH D cells.  I'm getting 3.8AH now in cells just a
>bit larger than AA cells.
>
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