On 2/26/10 10:25 AM, Don Zahniser wrote:
Hi, all -
I have Pismo that is behaving oddly with it's battery. It's a 'no-name'
battery, with a printed-on capacity of 6600mAH. I've had it for a
couple of years; it came with a Pismo that was bought as a Christmas
present for me by my Lady Technophobe. Utilities such as coconutBattery
do not read an original capacity for it; It currently shows a capacity
of 4128mAH - and I don't think it has really been much better than
that. Also - none of the utilities that read out the number of load
cycles display anything but zero.
Now - the odd behavior: When running from battery, I get about 2 hours
of steady use with Airport on - no problem with that, I suppose. The
oddity is that when the indicated capacity drops below about 30%, the
computer suddenly goes to sleep without any warnings. When I
immediately plug it in to the AC adapter, the capacity shows as 0%, and
climbs steadily.
I thought that the battery should drain further before sleep, and that I
should have at least one warning pop up beforehand.
I have tried resetting the PMU, which doesn't help. System info in signature.
In theory you are right, it should go down to 5 or 10% and then warn
you. Unfortunately batteries (the actual electo-chemical cells) don't
understand theory. :)
Capacity is based on the battery voltage. In an older battery there is
always one cell that dies sooner than the others. This causes the
battery voltage to suddenly drop. When it does the battery voltage goes
from a value that indicates 30% capacity to a value that means 0%
capacity. And the computer sense this and puts up the warning about low
capacity. The problem is that a circuit in the computer senses that the
supply voltage is too low and it shuts down the computer, before the
warning can go up. This is done to keep the hardware from
malfunctioning due to the low voltage, things like the harddisk randomly
erasing itself.
The basic problem is that the computer can't KNOW exactly when the power
will fail. It can make a guess which is what it does. When the battery
gets old and starts to flake out, that guess isn't very good.
You have two choices, use it as it is and be careful when the capacity
gets low or replace the battery.
--
Clark Martin
Redwood City, CA, USA
Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
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