Battery LED flashing

[Richard A. Smith]

On 01/02/2010 06:48 PM, Tabitha Roder wrote:

> resulted. We left it plugged in overnight and it appears to have charged
> normally and the battery now runs the laptop (when it was doing the
> flashing charge, the laptop would switch off immediately when you unplug
> the charger).
>
> http://wiki.laptop.org/go/Power_management#Battery_LED indicates
> flashing on charge means trickle charging. Sadly we didn't find this
> page when it was happening so cannot fully confirm it was flashing
> orange and with the 4 blinks, pause pattern.

I've updated troubleshooting guide to include the flashing yellow state.

The only thing that causes the charge LED to blink is trickle and error. 
  Flashing red is error so it was trickle.

'watch-battery' from the ofw ok prompt will also tell you "trickle" for 
the status when its trickle charging.

> This page also doesn't give
> any clues as to why a battery might be trickle charging.

Battery trickles when the voltage on the battery is < 5.4V.  This can 
occur if the battery is stored for a long time or if its installed in a 
(powered off) XO for > 30-50 days.  There is a small power drain even 
when the XO is turned off.

> http://wiki.laptop.org/go/Hardware_specification#Battery suggests that
> the battery has a Maxim DS2756
> <http://wiki.laptop.org/images/e/e9/DS2756.pdf> chip in it, but this
> chip only monitors one cell, so I guess there are two such chips?

No, the Cells are in series.  The sensor chip measures the voltage 
across both of them.  Overvoltage & undervoltage are monitored /cell by 
the safety monitor but there's no communication to that chip.

> The
> /sys interface only gives information about the whole battery, it
> doesn't tell you about the state of each cell.
> The specification pdf on
> the Hardware_specification page describes the Embedded Controller
> interface to the operating system in terms of "Battery", not "Cell" so I
> guess it doesn't expose each cell either?

The /cell info is not exposed because there's nothing available to 
expose and there's not much to do if they were.  There's only one path 
to the battery.  To do anything special you would need independent 
charging paths.

-- 
Richard A. Smith  <richard at laptop.org>
One Laptop per Child