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Re: Laptop Battery problem



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?  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.  

..lipo cells are lighter, popular with RC model pilots because they
recharge quickly, say 15 minutes, and can be drained safely down to
3V per cell, nominal voltage is 3.7V per cell, and most will charge 
up 4.1V, some even up to 4.3V per cell, and they require lipo chargers
which can be bought cheaply in model hobby shops, even online.

..beware that LiPo is slightly different from "Lithium Ion",
14.4V / 4cells = 3.6V, so where the lipo box _may_ need some 
more circuitry to tell the laptop the tall wallwart story, 
an old gutted NiCd battery case with new lipo cells _will_ 
need cheat circuitry to tell the laptop stories like below: 

  *-battery
       description: Lithium Ion Battery
       product: CP279034
       vendor: FUJITSU
       physical id: 1
       serial: 01
       slot: Internal Battery
       capacity: 74880mWh
       configuration: voltage=14.4V

> [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.

> (so no power-management
> stuff goes on) and see how it goes.
> 
> I'll have to look deeper into acpi which I guess could come in handy
> to try and gather some better information as soon as I'm back at the
> laptop and maybe report some results here.
> 
> Thanks for now,
> Lorenzo.
> 
> [1] 
> http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&docname=c00035862
> 
> 


-- 
..med vennlig hilsen = with Kind Regards from Arnt Karlsen
...with a number of polar bear hunters in his ancestry...
  Scenarios always come in sets of three: 
  best case, worst case, and just in case.


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