[ltp] Re: Thinkpad battery exhausted in less than a year?

[Theodore Ts'o]

On Mon, Nov 15, 2004 at 07:53:46PM +0100, Martin Gramatke wrote:
> 
> Meanwhile I had a phone call with IBM. They adviced me to remove the battery
> when the notebook is plugged in and in use. I should charge the battery
> only when the notebook is off. This is quite impractical. They also told me
> to do a total discharge every now and then.
> I can not believe that this is the right way, because I have never heard
> from other notebook users that they mount/dismount their battery all the
> time. The battery is also important to give the notebook a better stand.

Charging the battery only when the notebook will help, somewhat, but
my guess is that your main problem is the large number of
charge/discharge cycles.  That's pretty much guaranteed to wipe out
your batteries in very short order.  Really, you're going to to be
better off just simply keeping the notebook plugged into the AC mains
as much as possible.

> My idea to remove the plug when the battery is fully charged was to avoid
> these mini charge cycles. As you said, the battery will be no longer
> charged when it is at 100%, so it discharges. At a certain point, maybe 98%
> the battery becomes charged again and again...

Mini-charge cycles don't really damage the laptop all that much,
especially compared to the deep discharges.  Besides, the laptop
battery is smart about avoiding mini cycles.  If the battery
percentage is greater than 95% or so, it won't charge the battery up
to the full 100%, even when plugged into the AC mains, precisely to
avoid the mini-charge cycles (which again don't hurt as badly as
letting the battery discharge deeply and then recharging it).

The following note that Jan Kokoska sent out a few months ago has some
helpful information that may help you understand this situation
better.

Date: Sat, 25 Sep 2004 21:15:21 +0100
From: Jan Kokoska <kokoskaj@seznam.cz>
Subject: Re: [ltp] advanced battery recharge management
To: linux-thinkpad@linux-thinkpad.org
X-Mailer: Evolution 1.5.91

My mistake, I completely misquoted the material, which I subsequently
managed to find online [0]. The 40% is there, but meaning something
else.

Quote:

Li-ion batteries are not as durable as NiMH and NiCd designs, although
they do not suffer from the memory effect. At a typical 100% charge
level (notebook battery, full most of the time) at 25 degrees
centigrade, Li-ion batteries irreversibly lose approximately 20%
capacity per year from the time they are manufactured, even when unused.
(6% at 0 degrees, 20% at 25 degrees, 35% at 40 degrees centigrade. When
stored at 40% charge level, these figures are reduced to 2%, 4%, 15% at
0, 25 and 40 degrees centigrade respectively.) Every (deep) discharge
cycle decreases their capacity. The degradation is sloped such that 100
cycles leave the battery with about 75% to 85% of the original. When
used in notebook computers or cellular phones, this rate of
deterioration means that after two to three years the battery will have
capacities too low to be still usable.

--

Guidelines to prolonging Li ion battery life

      * Unlike nickel based rechargeable batteries (NiCd and NiMH), Li
        ion batteries should be charged early and often. However, if
        they are not used for a longer time, they should be brought to a
        charge level of around 40%. Never use the battery care functions
        some cellular phones provide for nickel based batteries. (This
        will deep cycle the batteries.)
        
      * Li ion batteries should be kept cool. Ideally they are stored in
        a fridge. However, they should not freeze. Aging will take its
        toll much faster at high temperatures. Keeping them in burning
        hot cars can kill lithium ion batteries.
        
      * Buy Li ion batteries only when needed. Look at the manufacturing
        date. That is when the ageing process commenced.
        
      * When using a notebook computer running from fixed line power
        over extended periods, it is advisable to remove the battery and
        store it in a cool place.

--

[0] http://www.fact-index.com/l/li/lithium_ion_battery.html


On Sat, 2004-09-25 at 20:26 +0200, André Wyrwa wrote:
> Hei,
> 
> On Sa, 2004-09-25 at 18:19 +0100, Jan Kokoska wrote:
> > I don't think this matters with LiIon batteries (unlike NiMH or NiCd),
> > there is no "memory effect" as in "shrinking maximum capacity" anymore.
> > There is only "remember maximum capacity and don't go over this when
> > recharging" effect [0] and you are recommended to completely flush the
> > battery once in a while and completely recharge it afterwards, so it has
> > a clear idea of how much should it recharge next time (). For regular
> > use the recommendation is to recharge with 40% remaining with complete
> > flush once in a few months. This all applies to LiIon which is in all
> > recent models (I wonder where LiPol is hiding, though). I am sorry not
> > to include links to the research papers I read this in, as I kept no
> > links and you can Google it as well as myself.
> 
> from what i've read, LiIon batteries loose capacity through permanent
> recharging when in almost full load state. This has nothing to do with
> memory effect. On that basis the option really affects battery life,
> since it avoids exactly that.
> 
> André.
> 
> 
-- 


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