Short circuting USB port?

[James Cameron]

G'day Timothy,

Thanks for getting back to me.  Pardon me for being fascinated, but it's
one of my pet topics.

The key to understanding this symptom might be the low voltage cutoff.
which is independent of the capacity indicator.

The "red battery light" is based on a calculation.  The calculation has
several sources of error, it is not perfect, and cannot be.  It's only
pretty good.  ;-)

But the low voltage cutoff is quite definite.  It happens if the voltage
drops below a certain point.  This can happen when the battery voltage
falls due to heavy load, if the battery connection falters, or if the
battery is removed.

Based on your new data, that AC was not plugged in when the symptom
happened, and you haven't been able to reproduce it, I think it is very
likely that the symptom was the low voltage cutoff triggering.  Had you
said AC was plugged in, I could almost certainly exclude the low voltage
cutoff.

That leaves the question ... why didn't the laptop tell you that the
battery was approaching that cutoff?  The battery state of charge
recorded in the battery management chip is not consistent with the
actual state of charge.  My guess as to the causes:

1.  a battery that is faulty,

2.  a charge and discharge cycle that was unusual,

3.  a USB device that is faulty, in that it draws more current than it
ought to do,

4.  dirt on the battery connector, or loose contacts due to lots of
removal and insertion of the battery in the laptop,

5.  not locking the battery fully into the laptop,

6.  battery management firmware that is faulty (we had some early
software faults ... but I don't know which faults might be in the
version you have)

The support team has a battery charge monitoring script, if I recall
correctly.

-- 
James Cameron    mailto:quozl at us.netrek.org     http://quozl.netrek.org/