Completely discharging LION batteries

Completely discharging LION batteries

[Frank Mehnert]

Hi,

I'm using Linux 2.4.20 together with the acpi patches 20021205-2.4.20 on a
Thinkpad T20. If I use two batteries (the builtin and a second in the Ultra-
Bay), the second battery first gets discharged _completely_ and after that
the internal battery is used.

The bad thing about that is that if I allow the Laptop to fully discharge
the LION battery, the usable capacity gets reduced. I have looked at
/proc/acpi/battery/BAT1/{state,info}: Before completely discharging the
battery, the "last full capacity" entry was about 30500 mWh. The design
capacity is 34560 mWh. After completely discharging the battery, the
maximum capacity to which the battery can be charged is only 28120 mWh,
so I lost about 2000 mWh or about 8 percent of the battery capacity!!!

So since I found that out I don't allow the Laptop to fully discharge the
battery anymore. So may questions are: Can I set the capacity at which the
Laptop switches to the builtin battery? Can you acknowledge my experiences?

Frank


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Re: Completely discharging LION batteries

[Matthew Garrett]

On Tue, Dec 10, 2002 at 08:59:52PM +0100, Frank Mehnert wrote:

> capacity is 34560 mWh. After completely discharging the battery, the
> maximum capacity to which the battery can be charged is only 28120 mWh,
> so I lost about 2000 mWh or about 8 percent of the battery capacity!!!

My understanding is that the microcontroller in the batteries IBM ships
only recalibrates capacity loss when the battery becomes completely
discharged. It's likely that your battery had lost 8% of its capacity over
a longer period of time, but only noticed this when it ran down
"completely" (where "completely" is the point at which the microcontroller
decides that the battery shouldn't be discharged any further, rather than
when there's really no charge left in it)

http://gimel.esc.cam.ac.uk/james/resources/tp240bat/bq2040.pdf is a
datasheet for the controller used in Thinkpad 240 batteries - it may well
be used across the rest of the Thinkpad range. A brief reading seemed to
suggest that the controller will stop charging the battery once it reaches
the "last full charge" capacity in the associated EEPROM, though I may
well be misreading that. You should be able to reprogram the EEPROM over
the SMBUS, but the Linux i2c drivers will refuse to load on Thinkpads due
to the possibility of killing the motherboard if the wrong address is
read.

-- 
Matthew Garrett | mjg59-1xO5oi07KQx4cg9Nei1l7Q@public.gmane.org


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Re: Completely discharging LION batteries

[Pavel Machek]

Hi!

> http://gimel.esc.cam.ac.uk/james/resources/tp240bat/bq2040.pdf is a
> datasheet for the controller used in Thinkpad 240 batteries - it may well
> be used across the rest of the Thinkpad range. A brief reading seemed to
> suggest that the controller will stop charging the battery once it reaches
> the "last full charge" capacity in the associated EEPROM, though I
> may

What is reason to stop charging early?
								Pavel
-- 
Worst form of spam? Adding advertisment signatures ala sourceforge.net.
What goes next? Inserting advertisment *into* email?


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AW: Completely discharging LION batteries

[Herbert Nachtnebel]

Hi!

> I'm using Linux 2.4.20 together with the acpi patches 
> 20021205-2.4.20 on a
> Thinkpad T20. If I use two batteries (the builtin and a 
> second in the Ultra-
> Bay), the second battery first gets discharged _completely_ 
> and after that the internal battery is used.

That's normal, but yes it is not the smartest idea to do.

> After completely discharging the battery, the
> maximum capacity to which the battery can be charged is only 
> 28120 mWh,
> so I lost about 2000 mWh or about 8 percent of the battery capacity!!!

Yes that's correct, but a 8 percent drop is way to much. 
It's a physical property that if Lion batteries are discharged 
completely the capacity gets smaller. Hence in areas were reliability is
important (i.e. in satellites) lion batteries are never allowed to discharge
deeply. But on the other hand, from the manufacturer point of view this is 
more than welcome. The customer has the replace his batteries sooner.

> 
> So since I found that out I don't allow the Laptop to fully 
> discharge the
> battery anymore. So may questions are: Can I set the capacity 
> at which the
> Laptop switches to the builtin battery? Can you acknowledge 
> my experiences?

The strategy is set by the BIOS or by the embedded controller, there is no
way to change it.

Herbert.


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Re: Completely discharging LION batteries

[Frank Mehnert]

On Wednesday 11 December 2002 10:26, Herbert Nachtnebel wrote:

> > I'm using Linux 2.4.20 together with the acpi patches
> > 20021205-2.4.20 on a
> > Thinkpad T20. If I use two batteries (the builtin and a
> > second in the Ultra-
> > Bay), the second battery first gets discharged _completely_
> > and after that the internal battery is used.
>
> That's normal, but yes it is not the smartest idea to do.

What I'm wondering about is that in the Windows 2000 Help of
the Thinkpad Laptop, IBM advises that it is better to discharge
the battery sometimes completely to refresh the full capacity
at least partly. That advise is completely the opposite of what
I've seen. But it could be an mistake in their documentation or
they could target NiMH batteries.

It is possible that there are some mechanisms that Windows knows
about and uses but Linux not?

Frank
-- 
Frank Mehnert
## Dept. of Computer Science, Dresden University of Technology, Germany ##
## E-Mail: fm3-IG//nw+yl+iQIjdd1DhZXWfrygkm6VTR@public.gmane.org    http://os.inf.tu-dresden.de/~fm3 ##


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Re: Completely discharging LION batteries

[Jochen Reinwand]

> > > I'm using Linux 2.4.20 together with the acpi patches
> > > 20021205-2.4.20 on a
> > > Thinkpad T20. If I use two batteries (the builtin and a
> > > second in the Ultra-
> > > Bay), the second battery first gets discharged _completely_
> > > and after that the internal battery is used.
> >
> > That's normal, but yes it is not the smartest idea to do.
>
> What I'm wondering about is that in the Windows 2000 Help of
> the Thinkpad Laptop, IBM advises that it is better to discharge
> the battery sometimes completely to refresh the full capacity
> at least partly. That advise is completely the opposite of what
> I've seen. But it could be an mistake in their documentation or
> they could target NiMH batteries.

Interesting informations about Li-ion batteries can be found at 
http://www.buchmann.ca/. It seems to be not available at the moment. But here 
are a few tips from the page:

- Charge the Li-ion often, except before a long storage. Avoid repeated deep
  discharges.
- Keep the Li-ion battery cool. Prevent storage in a hot car. Never freeze a
  battery. 
- If your laptop is capable of running without a battery and fixed power is
  used most of the time, remove the battery and store it in a cool place. 
- Avoid purchasing spare Li-ion batteries for later use. Observe manufacturing
  date when purchasing. Do not buy old stock, even if sold at clearance
  prices.

But there is also a note on the site that a deep discharge cannot bring back I 
higher full charge level. On this list I once found the tip that it should
work. I tried it and my battery was again able to charge to full capacity.
btw: DO NEVER COMPLETELY DISCHARGE A LI-ION! Normal electronic devices can not 
discharge a Li-ion completely. So it should be ok to discharge until the 
device powers of. There is still enough power in the battery to lit a lamp 
for a long time. But that would discharge it definitively to low!

Jochen


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