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Re: Laptop Battery problem



On 18/02/2012 22:36, Arnt Karlsen wrote:
On Fri, 17 Feb 2012 13:51:27 +0100, Lorenzo wrote in message
<4F3E4D4F.6090404@gmail.com>:

Hi Darac,

Thanks for the very insightful information...

On 17/02/12 13:38, Darac Marjal wrote:
On Fri, Feb 17, 2012 at 01:10:31PM +0100, Lorenzo Sutton wrote:
I am running XFCE 4.8 on debian wheezy on my laptop and since about
two weeks the xfce Power Manager gets the battery charge percentage
wrong, the most critical problem being that the machine shuts off
without any previous warning.

I wonder where the problem might be.

Indeed this  battery is getting old (3 years now) and less
efficient, but I can't explain why suddenly Xfce Power Manager is
getting it so wrong given that it was working like a charm (even
giving a pretty accurate esteem of remaining time). I imagine Power
Manager is relying on some lower level (software, kernel?)features,
maybe in the kernel?
I believe this is a common failing with batteries. I might be wrong
here, but as they age, the discharge profile of a battery changes
such that the monitoring hardware tends to over-estimate the
remaining capacity. This typically manifests as normal discharging
down to, say, 10 or 15%, followed by a sudden step to 0%.

Now, most power profiles are set up to warn of low battery at, say
10% and treat 5% as critical. If the battery capacity suddenly
drops past the warning level into the critical level, the system
has no choice but to take emergency measures.

As for where this information comes from: XFCE Power Manager will
query the ACPI daemon which is running in the background. That will
talk to the kernel's ACPI subsystem will, in turn, will talk to the
ACPI implementation in the BIOS. That, ultimately, is what decides
what the battery level is. Only the BIOS really knows what the
battery charge currently is, what a 'full charge' is and what 'zero
charge' is. It MAY be possible to re-teach the BIOS about the
current charge profile of the battery, but it's generally just
easier to increase the warning level in Power Manager.
HP advices a procedure (Windows only) to 'recalibrate' the battery

..what kinda battery, LiPo, NiCd, NiMH?

Li-ion

They have slightly different
discharge profiles, but "dive steeper" as they age.  If you can get a
new replacement or used spare battery from the vendor or Ebay, you can
then gut the worst battery and fit new cells into the gutted battery
housing.

..another way to extend laptop battery time, is stuff a laptop size
box full of lipo cells to match the charge plug voltage, and drain
the lipo box first, then have the laptop start draining its battery.


I've read about the freezer thing wonder if it works.

...


[2] I guess this could be reporduced in similar fashion. In
particular Option two could probably simply be boot into grub

..there's a game to play from grub, space invaders?
Can it be hacked to draw a discharge diagram in the background, or
write raw voltage, amperage etc numbers and timestamps to a file,
e.g. /boot/grub/batterydischargeprofile , ideally per cell?

:)


..batteries usually fails because _one_ cell fails, this can
be spotted early with load tests, the bad cell's voltage will
drop lower than the good ones.
Common lipo chargers can also be used to diagnose and prevent
this this failure mode.

and let
it stay there until it completely discharges

..this is a somewhat destructive test method, but it works on
NiCd and was recommended to "wipe the memory effect", 50%
discharges has a way of shaping the discharge curve so it
drops sharply beyond the 50% or whatever you discharged it
to, which has caused quite a few RC model aircraft crashes.

Only using it for boring spreadsheets ;)

Lorenzo.


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