XO battery/performance [Devel Digest, Vol 76, Issue 21]

Richard A. Smith richard at laptop.org
Fri Jul 13 23:34:27 EDT 2012

On 07/04/2012 12:20 PM, Yioryos Asprobounitis wrote:
> "0 bg-acr!" solved the problem of the erratic reading.
> Logs look more reasonable now (though there is still a sudden jump from 87 to 96% during charging in one log.

Thats normal.  There isn't any calibration of the capacity as the 
capacity of the battery decreases.  So while charging its going to reach 
full sooner.  When its full the SOC is set to 97%.

> Battery capacity looks also improved (2.8Ah in one run)

I don't see any of your logs that have 2.8Ah they all look like 2.5Ah 
and 2.6Ah to me.  Which log are you referring to?

> However, the original issue of battery losing ~12% charge per day while in the XO with the laptop off, is there.

There is certainly something up with your battery.  The charging log 
shows where the problem is.  Look at line 386 in 
pwr-120703-010410-355aaa2500000043.csv . Thats where the battery stop 
reaches its full condition (Voltage@ 7.4V and current < 120mA). 
Normally the status would switch to Full and the current would bounce 
around very close to zero.  Your battery however has a constant 
discharge current of 16mA.  So despite having the power connected your 
battery is slowly discharging.  This seem strange but its possible 
because when the EC detected the battery was full it turned off the 
mosfet that is in the charging path.  So the battery is isolated from 
the system.  Only when you unplug power does the mosfet re-engage so the 
battery can then supply power.

If you want to prove its the battery then try the same test on other 
XO-1s and on your 1.75.  Another test you could do is to see if the ACR 
changes with the battery removed from the laptop.  You can do this with 
batman.  The steps would be:

1) Connect XO 1 or 1.5 to external power.
2) Boot the machine and stop at the open firmware prompt
3) Allow battery to charge up up until full.
4) print out the ACR with:
   ok bg-acr@ .bg-acr
5) remove battery
6) record the printed ACR number somewhere
7) Note time of battery removal
8) Wait 24 hours.
9) repeat steps 1-4
10) subtract the 2 ARC numbers to the the net ACR.

According to your log your average draw is 16.4mA.  So if you let it sit 
for 24h I would expect your net acr to be in the range of 390 - 400 mAh 
(the number is in uAh so thats 390000 to 400000)

If it happens outside the XO then you know its in the battery. If not 
then its some interesting combination of battery and XO.

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

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