[TriLUG] battery life [ Was Re: laptop battery replacement, where to buy? }

[Joseph Mack NA3T]

On Sun, 27 Mar 2011, Joseph Mack NA3T wrote:

picking up a thread from Feb, where a bit of searching with 
google found that if you kept your laptop battery below 80% 
charge (rather than 100% and preferably 50-80%) that your 
battery life was enormously extended, from 18mo to way 
beyond the expected useful life of the laptop (about 4yrs I 
remember). There were charts of life as a function of 
charging level

eg
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

I know that satellites and hybrid cars carefully monitor 
charging levels to increase battery life, so battery 
university isn't the only place pushing lower charging. 
Keeping your battery charged at 50-80% seemed to be a 
no-brainer and I changed the battery charging settings on 
the spot (I used thinkpad smapi).

Here's the rrdtool record of the life remaining in my 
battery (life == green dots. The laptop has to be on 
continuously for about 2 days to get a dot on the yearly 
chart, so there's only a few points).

http://www.austintek.com/battery/battery-year.x60.gif

I started recording in Oct 2010, when I got the laptop. In 
Feb 2011 I changed from full charging (to 100%) to keeping 
the battery between 50-80% (seen by the red dots). The 
laptop is used as a portable (ie it's almost always plugged 
in somewhere), rarely used on battery and never sits in a 
hot car (which stews the battery).

I was looking for a 2- to 4-fold increase in battery life. 
The slope of the green line (life of the battery) is 
constant (didn't change in Feb) i.e. there hasn't been any 
change in the rate of decline of the life of the battery as 
a result of charging between 50-80%. From the slope of the 
line I expect to get 2yrs out of the battery if I use 50% 
capacity as end-of-life.

I have no idea why the change in charging regime hasn't 
helped my battery life. I can't imagine that the charts are 
made up. The battery university site measures life of the 
battery in charge/discharge cycles (if you discharge/charge 
20% for 5 times, it's counted as 1 cycle). I'm not cycling 
my battery. It stays at 80% for nearly all the time.

Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!