[Ti] Conductivity/Battery Charging

[Kynan Shook]

Doffie Rotter <doffie.rotter at uconn.edu> writes:
> One more addendum to the heat issue:  When running on battery, this PB
> is just barely warm!  It's hottest when it's _actively_ charging (i.e.,
> when plugged in and under 100% charged).  When it's plugged in and the
> power cord glows green (fully charged), it is slightly less hot.
>
> Someone writing in a Readers' Report on the Macintouch site made a
> similar observation, but also reported that sometimes the battery
> indicator won't go all the way up to 100%, and it seems that the
> machine is going to keep charging without end.  I have not had that
> experience.


Well, I don't know too much about the chemistry involved in 
rechargeable batteries, but I can tell you that your observed behavior 
makes sense with what you would want the case to be ideally; feeling 
heat on a part means that it is dissipating some power.  When you're 
running on battery power, you want to minimize the power used (and 
therefore the heat dissipated), especially on parts that aren't really 
doing anything; in other words, you want the chemical reaction in the 
battery to produce only electrical energy, and not heat energy.  If it 
were producing heat, it would be wasting some of its stored energy.  
However, when you're plugged in, you don't care very much if the 
battery needs extra power to charge; it can just draw a little more 
from the power adapter.  Because of the extra power the battery is 
drawing while charging, the rest of the computer (especially the area 
around the DC power plug) will heat up too as it is handling more power 
input than normal.  This is one reason why the area around the power 
button on TiBooks has always been warm, though Apple eventually placed 
a fan in that area.

As for the guy on Macintouch, I read his (her? I don't recall) story, 
and it sounds like it may be a possibility of him being excessively 
picky and normal behavior; all laptops after the original G4 series 
with original batteries will not necessarily charge all the way to 100% 
to avoid short recharge cycles which can shorten the battery life.  The 
computer will wait until the battery drops below about 95% to charge it 
back up to 100%.  It could also be that he has a faulty battery or his 
power management needs to be reset.


Kynan Shook
kshook at mac.com
http://homepage.mac.com/kshook/index.html