[iBook] Newbie: age old question concerning battery

[Jay Hill]

>Lithium-ion batteries do not suffer from the memory effect: topping
>them up before they are fully discharged does not shorten battery life.

Well... I didn't want to get too technical for the newbie, but here goes....

Although lithium-ion is memory-free in terms of the performance
deterioration that plagues NiCad and NiMH batteries, lithium-ion batteries
with fuel gauges (like laptops) exhibit what engineers call "digital
memory". 

Here is the reason: Short discharges with subsequent recharges like the
original poster described do not provide the periodic calibration necessary
to synchronize the fuel gauge with the battery's true state-of-charge.

A deliberate full discharge and recharge every so often corrects this
problem. Letting the battery run down to the cut-off point in a notebook
will do this nicely. If ignored, the fuel gauge will become increasingly
less accurate.

> According to Apple's site,
> you get so many "full charges" per battery. So if you drain half the
> battery, then recharge it, then drain half again some other time and
> recharge, that's one full charge. In other words, it's no longer necessary
> to run your battery all the way to empty before recharging.

Apple recommends charging and discharging its battery once per month to
'keep the electrons in it moving.' Also, Apple does not recommend leaving a
laptop plugged in all the time.  Although the article at
http://www.apple.com/batteries/notebooks.html does not expressly recommend a
FULL battery discharge, I would assume the word 'discharge' means to the
notebooks cut-off point not to a 50% charge.