<link>http://people.skolelinux.org/pere/blog/</link>
+ <item>
+ <title>The life and death of a laptop battery</title>
+ <link>http://people.skolelinux.org/pere/blog/The_life_and_death_of_a_laptop_battery.html</link>
+ <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/The_life_and_death_of_a_laptop_battery.html</guid>
+ <pubDate>Thu, 24 Sep 2015 16:00:00 +0200</pubDate>
+ <description><p>When I get a new laptop, the battery life time at the start is OK.
+But this do not last. The last few laptops gave me a feeling that
+within a year, the life time is just a fraction of what it used to be,
+and it slowly become painful to use the laptop without power connected
+all the time. Because of this, when I got a new Thinkpad X230 laptop
+about two years ago, I decided to monitor its battery state to have
+more hard facts when the battery started to fail.</p>
+
+<img src="http://people.skolelinux.org/pere/blog/images/2015-09-24-laptop-battery-graph.png"/>
+
+<p>First I tried to find a sensible Debian package to record the
+battery status, assuming that this must be a problem already handled
+by someone else. I found
+<a href="https://tracker.debian.org/pkg/battery-stats">battery-stats</a>,
+which collects statistics from the battery, but it was completely
+broken. I sent a few suggestions to the maintainer, but decided to
+write my own collector as a shell script while I waited for feedback
+from him. Via
+<a href="http://www.ifweassume.com/2013/08/the-de-evolution-of-my-laptop-battery.html">a
+blog post about the battery development on a MacBook Air</a> I also
+discovered
+<a href="https://github.com/jradavenport/batlog.git">batlog</a>, not
+available in Debian.</p>
+
+<p>I started my collector 2013-07-15, and it has been collecting
+battery stats ever since. Now my
+/var/log/hjemmenett-battery-status.log file contain around 115,000
+measurements, from the time the battery was working great until now,
+when it is unable to charge above 7% of original capasity. My
+colletor shell script is quite simple and look like this:</p>
+
+<pre>
+#!/bin/sh
+# Inspired by
+# http://www.ifweassume.com/2013/08/the-de-evolution-of-my-laptop-battery.html
+# See also
+# http://blog.sleeplessbeastie.eu/2013/01/02/debian-how-to-monitor-battery-capacity/
+logfile=/var/log/hjemmenett-battery-status.log
+
+files="manufacturer model_name technology serial_number \
+ energy_full energy_full_design energy_now cycle_count status"
+
+if [ ! -e "$logfile" ] ; then
+ (
+ printf "timestamp,"
+ for f in $files; do
+ printf "%s," $f
+ done
+ echo
+ ) > "$logfile"
+fi
+
+log_battery() {
+ # Print complete message in one echo call, to avoid race condition
+ # when several log processes run in parallell.
+ msg=$(printf "%s," $(date +%s); \
+ for f in $files; do \
+ printf "%s," $(cat $f); \
+ done)
+ echo "$msg"
+}
+
+cd /sys/class/power_supply
+
+for bat in BAT*; do
+ (cd $bat && log_battery >> "$logfile")
+done
+</pre>
+
+<p>The script is called when the power management system detect a
+change in the power status (power plug in or out), and when going into
+and out of hibernation and suspend. In addition, it collect a value
+every 10 minutes. This make it possible for me know when the battery
+is discharging, charging and how the maximum charge change over time.
+The code for the Debian package
+<a href="https://github.com/petterreinholdtsen/battery-status">is now
+available on github</a>.</p>
+
+<p>The collected log file look like this:</p>
+
+<pre>
+timestamp,manufacturer,model_name,technology,serial_number,energy_full,energy_full_design,energy_now,cycle_count,status,
+1376591133,LGC,45N1025,Li-ion,974,62800000,62160000,39050000,0,Discharging,
+[...]
+1443090528,LGC,45N1025,Li-ion,974,4900000,62160000,4900000,0,Full,
+1443090601,LGC,45N1025,Li-ion,974,4900000,62160000,4900000,0,Full,
+</pre>
+
+<p>I wrote a small script to create a graph of the charge development
+over time. This graph depicted above show the slow death of mylaptop
+battery.</p>
+
+<p>But why is this happening? Why are my laptop batteries always
+dying in a year or two, while the batteries of space probes and
+satellites keep working year after year. If we are to believe
+<a href="http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries">Battery
+University</a>, the cause is me charging the battery whenever I have a
+chance, and the fix is to not charge the Lithium-ion batteries to 100%
+all the time, but to stay below 90% of full charge most of the time.
+I've been told that the Tesla electric cars
+<a href="http://my.teslamotors.com/de_CH/forum/forums/battery-charge-limit">limit
+the charge of their batteries to 80%</a>, with the option to charge to
+100% when preparing for a longer trip (not that I would want a car
+like Tesla where rights to privacy is abandoned, but that is another
+story), which I guess is the option we should have for laptops on
+Linux too.</p>
+
+<p>Is there a good and generic way with Linux to tell the battery to
+stop charging at 80%, unless requested to charge to 100% once in
+preparation for a longer trip? I found
+<a href="http://askubuntu.com/questions/34452/how-can-i-limit-battery-charging-to-80-capacity">one
+recipe on askubuntu for Ubuntu to limit charging on Thinkpad to
+80%</a>, but could not get it to work (kernel module refused to
+load).</p>
+
+<p>I wonder why the battery capacity was reported to be more than 100%
+at the start. I also wonder why the "full capacity" increases some
+times, and if it is possible to repeat the process to get the battery
+back to design capacity. And I wonder if the discharge and charge
+speed change over time, or if this stay the same. I did not yet try
+to write a tool to calculate the derivative values of the battery
+level, but suspect some interesting insights might be learned from
+those.</p>
+</description>
+ </item>
+
<item>
<title>Book cover for the Free Culture book finally done</title>
<link>http://people.skolelinux.org/pere/blog/Book_cover_for_the_Free_Culture_book_finally_done.html</link>
projects / homepage.git / blobdiff