Mac Forum / General / Portable Macs / August 2006

... but for a very different reason.

Which ones now, Li-Ion or NiCd?

"In contrast to nickel-based batteries that require full discharges to
keep the battery healthy, lithium ion batteries are better with
frequent, shallow discharges before charging again."

I don't think that this is right. I read claims that only a certain
limit of charge cycles is applicable for Li-Ion - and even a partial
charge cycle will count (almost) as a full charge cycle.

Different reasons - they degrade just by age. After two years, about
80 % are left, and there's not much to do after five years, even without
usage.

That's completely different than Lithium throw away cells which have a
very high reputation for long time storage.

The charge and discharge logic for thos batteries is pretty simple. You
may charge up to a certain level fast, while the final charge should be
done with smaller currents. There's a certain voltage limit per cell
which never must be exceeded. There's a certain deep discharge level
which will damage the cell. Batteries don't like high temperatures.
But while these limits have to be maintained per cell, which is why
there's lots of charge and discharge control within the battery pack, it
seems to be pretty easy.

For iBooks 10.8 V you have 3 * 3.6 V in series - and every one has to be
ok.

For NiCd you had e.g. 14.4 V, which is 12 * 1.2 V cells in series. NiCd
may be discharged down to 1 V per cell - thus 12 V here for the full
pack are still ok. It's not even bad when you discharge the cell
completely down to 0 V. But at this moment, when other cells in this
series are still stronger, it may occur that the cell voltage of the
weakest cell is reverted - and this will damage the cell significantly.
It won't do much harm, other than a little bit of heat. But you'll never
again be able to obtain the full capacity, since this single, damaged
cell will loose its capacity very fast again when discharging.

So a deep discharge of the NiCd is more or less ok. But for Li-Ion you
have to take care that both charge and discharge of each cell is within
the limits.

However, what went wrong here: As far as I know there's some unwanted
impurities within these Sony cells - some kind of unwanted metal which
came in within the production process. This is the claimed reason why
the cells here failed that dramatically (cpsc named 9 cases for Apple, while
there's a video of the burning Dell laptop which happened within a
conference).

LiIon offers higher capacity than NiMH - and this one has higher
capacity than NiCd, which again is superior to Lead Acid, just to name
the most common. It's almost the inverse order, concerning ease of use
and price.

LiIon is good for current Laptops. It's bad when you won't obtain spare
batteries after the next 5 years. And it's bad when you can't exchange
the battery at all (e.g. iPods, even worse for the iPod Nano).

LiIon had some heavy accidents e.g. within mobile phones (sometimes
claimed due to 3rd party batteries). So LiIon per se is not critical.
However, when the battery itself is faulty, you can't do much against
it. You can't even trust so called quality labels, such as Sony here.
But what's your alternative?

I don't see any for laptops. There's not much for mobile phones. There's
not much for higher level mp3 players. I see most choice e.g. for
digital cameras, which can be driven either by Li-Ion or standard AA
cells (NiMH most of the times now).

'amazing' may be the wrong term - I'd say it's frightening. Fortunately,
mercury is gone by now from most of the batteries. Nickle Metal Hydride
is better than Nickle *Cadmimum*. But still Nickle is bad enough -
batteries should be collected and returned. Is this the common standard
in the US, too, to return them within every shop?

- Martin

I'm fully aware of that.  Their hardware (both computer and
home-entertainment equipment) has turned to utter crap over the past
couple of years, which has kept me away from it. The rootkit fiasco has
kept me from their entertainment division.  What's left?

Correct.  Deep-discharging a lithium battery will shorten its life more
than multiple partial-discharges.  The complete opposite of the old
nickel-based batteries.

Battery University's page on lithium is also excellent:
http://www.batteryuniversity.com/parttwo-34.htm

 Apple updated their web pages. Nows some of the serial numbers have
additional qualifications. For the A1061 model for the 12" iBook B4, it
says: "6C519 - 6C552 ending with S9WA, S9WC or S9WD". My serial number
falls within the range but ends with S9YD, so I guess we are not subject
to the recall.

-R.

[removing battery to check its serial number while running]

The Apple System Profiler takes care of that here. Under Hardware
Overview.

Lara