geoff winkless

Hi

I have a Thinkpad I've just got for a friend from ebay.

After a full recharge the battery meter reports 58 minutes of battery life,
which it then counts down and duly shuts off the laptop at 3% as per power
settings. However, if I turn off all the power sense and just let the thing
run until the battery actually shuts off, it runs for more than twice as
long - over two hours.

I've tried about 5 full-charge (overnight) and full-discharge cycles as
recommended by the Thinkpad battery help, but the values don't seem to
change: 14kWh maximum charge is reported (rated amount for the battery is
apparently 40kWh , IIRC). I don't want to keep full-cycling because I had
though that with Lions this actually does more harm than good.

I'd assume it was the internal battery circuitry which was getting it wrong
except surely then it would cut off power earlier? Or is the protection
circuitry different to the guage which reports the charge held?

I can pick up a nearly-new battery for not much (about £30), so it's not a
major issue... but it bugs me that chemically the cells are obviously much
better than they report, but I can't just turn off the laptop's power sense
and use it because then you can guarantee the power will cut just at the
wrong moment!

Thanks

Geoff

mark w. lund, phd

Battery fuel gauges are the bane of my existence, it is very
difficult to make them accurate at all, and even more difficult
to do it for a battery that is long in the tooth.

Some of the chips will recalibrate under the cycling you describe, I
would have expected that a thinkpad would have this kind of
circuit, but evidently not.

When people start using the new techniques developed by TI
it should improve the accuracy.

BTW, should be 40 watt hours, not 40 kilowatt hours.

Best regards
mark


--
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Mark W. Lund, PhD ** Battery Chargers
CEO ** Bulk Cells and Custom Battery Packs
PowerStream Technology ** Custom Power Supplies
140 S. Mountainway Drive ** DC/DC Converters
Orem Utah 84058 ** Custom UPS
http://www.PowerStream.com ** Engineering, manufacturing, consulting

evgenij barsukov

That is a problem that is becoming recognized - gas-gauging algorithms
are starting to underestimate capacity more and more as battery ages.
As result battery is reported dead while it is alive and well.
The real solution for this is a gas-gauge that continuously updates
its battery model to take into account battery impedance increase. Such
gas-gauging IC (bq20z80) is now going into mass production in TI:
http://www.analogzone.com/pwrp0913.htm

For the older battery packs, there is a way to disable shut-down of your
notebook (go to windows power properties, and unckeck all the actions on
"depleated" alarm). However, some BIOSes are still going to shut-down
the notebook even if Windows will not.

Regards,
Evgenij