test result of battery current against display brightness and GPS power mode

mqy meng.qingyou at gmail.com
Fri Mar 27 14:23:28 CET 2009

Thanks for the tip.

My previous test program is written in C. I write a bash script and test again.
GPS, WIFI, bluetooth, GSM, xserve, fso-frameworkd, python, batget are disabled/closed.
OS suspending is disabled in SHR settings.
With top command, I watch for a while to make sure no process other than top and dropbear 
using more than 0.1% CPU cycles. Then start the script and unplug USB.

for ((i=0; i<120; i++)); do
  sleep 30 
  echo "i = $i:"
  cat /sys/class/power_supply/battery/{current_now,capacity,voltage_now}

The result is almost same with my previous test, on newly updated SHR:

Within 60 minutes, capacity drops from 100% to 91%, voltage drops from 4.16 V to 4.06 V,
current increases from 103.5 mA to 104.5 mA, 

On Fri, Mar 27, 2009 at 05:21:59AM +0800, Qingyou Meng wrote:

>    To save power, we set display brightness to 0% by locking screen,
> but OS still consumes 95 mA, leaving at most ~10 hours battery life!

   You must have done something wrong. I frequently test power comsumption
and I get 54 mA on a fully charged battery, dropping slowly as the battery
discharges[1] and nearly 20 hours battery life.

   FWIW, I test with this command on a Debian installation:

sleep 120 && cat /sys/class/power_supply/battery/{status,current_now,voltage_now,capacity}

[1] It's supposed to be the other way around - current increasing as the
battery discharges - but there's a current leak somewhere. It was down to 46
mA not too long ago with a kernel from the andy-tracking branch.

Rask Ingemann Lambertsen
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