Document with answers to most popular battery-related questions is ready

Rask Ingemann Lambertsen ccc94453 at
Sun Aug 9 13:37:00 CEST 2009

On Mon, Aug 03, 2009 at 01:46:26AM +0800, Wolfgang Spraul wrote:
> How are people really using the Coulomb counter in gta02?
> Theoretically I would think that it provides far superior power measurement
> options for actual software development, just as you write.
> For example when playing with power saving codes, whether in the kernel,
> middleware or applications, I would think over the course of several hours or
> days the Coulomb counter data is the primary means for efficient development.

   To me: The clearly most useful part of the bq27000 is the current
measurement. You get what seems to be a reasonably accurate measure of the
current flow to/from the battery updated every 25 s or so. It's much more
practical than an external ammeter: No need to open the case and fiddle with
probes, you can measure battery current while in the train, at work or
wherever. Having it built in makes accurate current measurement available to
many more people in a lot more places.

   Here's a few examples where the current measurements have proven useful:
1) Tracking down that current leak from the serial ports into the Calypso.
2) Finding that 8 mA apmd current leak Debian used to have.
3) Confirming the server screen blanker current leak of 38 mA.
4) Measuring the effectiveness of reducing CPU clock and core voltage.

   Hopefully it will also help to curb assorted forms of spyware because
they will be easier to detect with the power consumption figures readily

   I don't think it is worth it to spend a coulomb counter on each battery.
The selling point would be to keep track of battery degradation, but I've
already seen it change its mind from 1067 mAh to 1148 mAh - that's an error
of two hours worth of idle time at 100 MHz.

   To get a charge level reading, add a voltmeter connected to the battery
terminals. As long as the charge and discharge rates are moderate, it will
be good enough.

Rask Ingemann Lambertsen
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