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Re: Should I completely discharge my laptop battery?

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On 12/30/2014 4:35 PM, ~misfit~ wrote:
> Once upon a time on usenet andymhancock@gmail.com wrote:
>> I have a Satellite A660 laptop with a Lithium-Ion battery pack.  I've
>> read that you should completely discharge batteries every month so
>> that the charger can recalibrate on what is 0% versus 100%.  Does this
>> apply to Lithium-Ions?
>
> Yes, especially to Li-Ion as they last so long that the control circuitry
> needs new info on the state of the cells from time to time.
>
>> This also means I turn off the safety feature
>> of hibernating when the charge dwindles to 8%.
>
> Yes.
>
>> Doesn't the disk heads crash once the charge dies?
>
> No. Newer laptops are clever enough to stop in a controlled manner as the
> battery pack is exhausted. This is another good reason to fully discharge
> your battery now and then - so the control circuitry knows at what voltage
> it's near-empty.
>
I have a contrary opinion.
I don't have any NEW systems, so this is slightly out of date,
but the concepts haven't changed.
Surely someone will come up with a counterexample that proves me stupid,
so, you'll have to decide whether you believe me.

I've only done this on a dozen or so batteries, so can't guarantee all are
that way.  All this assumes that a worn battery is just worn and does
not have shorted cell and not part of a stupid system design
that puts some of the cells right adjacent to the processor heat sink
and cooks them.

There are at least three levels of protection.
A coulomb counter basically counts the electrons as they go in/out.
Knowing the battery capacity, you can calculate the state of charge.  I 
believe the laptop polls the battery to determine
the state of charge and decides what to do.  That's an orderly shutdown
or hibernation as you've instructed in the setup.  There's likely a
voltage threshold too.

Battery and laptop vendors are very concerned that you don't sue them
over battery issues aka fires.  They care not that you have to buy
a new battery.  At retail, they probably make more profit off the
battery than they did on the laptop.  I read it on the internet so it
must be true.

There are at least two other discharge protections in the battery pack.
There's a shutdown voltage below which the control FETs open up and 
disconnect
the battery.  This is NOT a controlled shutdown.  The battery just 
disconnects.  This is likely what you get when you turn off the protection
and run it till it quits.

There's a end of life voltage below which the pack will not recover.
You can't normally (see below) get there by discharging.
But you can get there
by sticking a discharged battery in the drawer for a couple of years letting
the discharge protection circuit systematically discharge the cell.
Sometimes it's firmware in the microcontroller that cannot be
reset unless you know the secret method and can reprogram it.
I've seen some that have a thermal fuse adjacent to a resistor.
At the end of life
threshold, they light up the resistor and blow the thermal fuse.
In either case, that battery pack ain't coming back.  The only pack
I've ever recovered had a PIC processor as controller and hitting
the reset did actually reset it.

Some of the old dell dimension packs would let you open them up,
charge the cells directly and they would run the computer again.
They'd continuously flash an error code and the battery gauge didn't
work, but you could run the computer.

I think it was a Toshiba that had an end of life mode that would
let you run the laptop off the battery.  OR, you could charge the
battery with the computer off.  If you wanted to run the laptop
off AC, you had to physically remove the battery.  Strong motivation
to buy a new battery, or in my case, strong motivation to never buy
another Toshiba.

I don't think I ever got a Thinkpad battery back.

So, why do batteries fail?
Over time, the cells just can't store as many electrons and capacity
decreases some.
But my experience is that the primary failure is due to increased
internal series resistance.
The symptom is as follows...
You charge the pack and the battery level shows 100%.
You disable the battery warning modes.
You run the computer and the meter drops steadily like
you'd expect until it hits some level like 40% and drops
immediately to zero and the computer shuts down soon thereafter.

If you take the battery out and test it under controlled conditions,
you find that most of the electrons are in there and can be recovered
at low current.  If you load with high current, the current x high 
series resistance
subtracts from the voltage to the point that the protection circuit
shuts you down at shutdown voltage.  The electrons are in there, but
the pack won't let you take them out.

Now, we get to the relevant part.
I've had a two systems that had about 50% usable battery capacity.
I decided I'd discharge them in hope of resetting the battery gauge.
I turned it on and let it sit till it quit.  And it never came back.

Here's my thesis.  I think the system sat there at low power with the
display backlight and hard drive off until it hit the point where the
laptop decided to take some action. Most of the capacity was gone.
When the disk started and the backlight started, the additional voltage
drop due to the increased current in the high battery internal series 
resistance
dropped the battery voltage all the way to the end of life threshold.
Game over.

That's why I'm very wary of running systems 'till they quit.  Seems to
work fine on slightly used batteries.  When the resistance gets high,
you may just kill a perfectly half-good battery.

If it ain't broke, don't fix it.

YMMV

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Thread

Should I completely discharge my laptop battery? andymhancock@gmail.com - 2014-12-30 11:53 -0800
  Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2014-12-31 13:35 +1300
    Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2014-12-31 11:06 -0800
      Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2014-12-31 11:54 -0800
        Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-01 15:13 -0800
      Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-01 12:29 +1300
    Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2014-12-31 12:05 -0800
      Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-01 12:55 +1300
        Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-01 14:51 -0800
          Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-02 14:16 +1300
            Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-01 18:11 -0800
              Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-02 01:15 -0800
                Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-02 09:34 -0800
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-02 10:46 -0800
                Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-02 14:25 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-04 12:28 +1300
                Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-03 16:48 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-07 14:47 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-06 19:38 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-09 13:36 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-08 17:34 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-10 14:59 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-09 20:22 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-13 12:18 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-12 17:20 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-15 13:35 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-14 17:37 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-16 12:33 +1300
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-02-08 14:24 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-02-07 21:02 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-02-11 11:09 +1300
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-03 11:47 +1300

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