[Novalug] Re: [Dclug] Power Critically Low, Not.
przemek at jazz.ncnr.nist.gov
Thu Nov 16 14:34:34 EST 2006
When I unplug the AC power on my HP laptop (Running Fedora 5), I get a message
saying something like "Warning, power is critically low, you have 4 minutes
remaining, battery power 98%".
Clicking on it again says 3 hours, 13 minutes, 98%.
Anyone have any idea on what I can do to investigate what is going on more..?
I'm wondering if there is some sort of ACPI tracking that "thinks" my 98% will
only last 4 minutes..
I think what happens is that your battery drops voltage a little bit
when disconnected from charging. The charge controller sees a
momentary change from 100% to 98% in the 5 second interval between its
successive measurements of the voltage, and extrapolates that to 0% in
5*50 seconds, i.e. around 4 minutes. At the next measurement few
seconds later, it's still 98% so the new slope is zero or some
weighted average, and it calms down.
Maybe there is a parameter in the battery applet or the APM/ACPI
driver that increases filtering so that it can survive 2% jumps w/o
getting confused about the discharge slope. Ideally, you'd force the
battery controller to learn the full-charge voltage of the
battery---some controllers do that if you let the battery to do a full
discharge/recharge cycle. My /proc/acpi/battery/BAT1/info says:
design capacity: 38888 mWh
last full capacity: 37286 mWh
so it knows that the full charge is less than the design charge.
What do you get?
By the way, 38 W hr an energy equivalent of 30 grams of TNT or
over a gallon of natural gas. Respect your batteries.
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