power consumption after shutdown

[quozl at laptop.org]

On Sat, Feb 14, 2009 at 01:56:22PM -0500, Mikus Grinbergs wrote:
> I have found the XO-1 batteries (mfg by BYD Company Ltd) to be very 
> stingy with energy loss.  When I put one back in after a month out 
> of the case, the XO software told me it was still 94% charged.

The displayed state of charge is stored in the chip in the battery, and
is maintained by the EC.  The battery does not change it's own state of
charge value.

I don't think that batteries outside the XO will have their state of
charge value changed by the chemical self-discharge process.  But once
the terminal voltage becomes significantly inconsistent with the state
of charge value, I imagine that the terminal voltage is trusted more.

(If one discharges an XO battery outside the XO using a home lighting
circuit, the displayed state of charge will be inconsistent.  Persisting
in this practice results in increasing inconsistency.  Ceasing the
practice results in decreasing inconsistency over several XO moderated
charge and discharge cycles.  The inconsistency results in forced
power-down before the state of charge would suggest, manifesting as "my
XO stops too soon".)

> James Cameron mentioned measuring a current draw of 24mA.  I suspect 
> this was *not* on a thoroughly "shut-down" G1G1.

Wrong.  It was on a thoroughly shutdown mass production unit.  The unit
was shutdown using the Sugar shutdown option, then the DC cable and the
battery were removed, 30 seconds were allowed to elapse, and then the DC
cable was reinserted.  The measurement was after this reinsertion.

> In my experience, 
> after two days in a "shut-down" state the XO software shows the 
> battery charge % to be somewhere in the mid-90's.

You observe a difference between my measurements and yours.  I knew the
technique was inadequate, but I was providing it as a maximum.  I had
already said that I thought the external DC supply path to contain
additional losses.  Richard has explained that the difference was due to
the EC not stopped, because it knows it is on external DC supply.

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