Wednesday, November 11, 2009

Battery Capacity Logger

I just replaced the battery in the 2005 ibook G4 today, great to return to the days of 4 hours of use. I decided I'd like to monitor the life of the battery and so wrote a quick cron job script to log the battery capacity every day. I also have installed this on my main laptop which still gives me 3 hours after 18 months of use.

Write the script.
# : Log battery capacity to a file
date >> ~/batteryCapacityLog.log
system_profiler SPPowerDataType | grep "charge capacity" >> ~/batteryCapacityLog.log

Make it executable and put somewhere sensible.
chmod 755
cp /usr/local/bin/

Make sure it is activated daily by adding the following line in crontab using crontab -e which will make it run at 5:10am every day. This time is chosen to not clash with other actions executing should my laptop be awake at 5am and also to ensure it run each morning when I wake the laptop up.

10 5 * * * /usr/local/bin/

The format looks like the following:

Wed Nov 11 20:03:26 GMT 2009
Full charge capacity (mAh): 4859
I may improve the format in the future and add some nice "gnuplot" plots but this gives me the info I want right now. For the record, the outgoing battery was showing a capacity of around 350mAh. This translates to roughly 10-15 mins of use. OS X 10.5.8