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

Richard Smith richard at laptop.org
Wed Jul 18 16:22:35 EDT 2012

> On an XO-1
> The reading is "-4610.42" (!?)

Its a 2's compliment number. Negative values are normal.  But you need
more than 1 reading.  A single reading of the ACR doesn't tell you
anything unless you reset it to a known value before you start.

> Reboot to Sugar and got "very little battery"
> At no point the charge light came up (green, red, or orange/yellow)
> run 0 bg-acr! and then bat-recover. Indeed the battery looked drained (6.9 Volts) and charged but took took just few mAh before it jumped to 7.4 volts. Still no battery LED

We are running debugging commands outside the EC.  All reporting
normal battery status reporting is invalid until you run a discharge
and recharge cycle
Also bat-recover is useless for this problem.

> I may be way off, but judging from the erratic readings and LED behavior I would think that might be an issue with the battery EC. Anyway to "talk" to it and make it behave?

Yes you are way off because you don't understand what you are doing.
I'll be more specific in my instructions.

> Though if interested I think would be much more efficient if you check the battery in person ;)

I'm mildly curious but what if you send it to me and then the problem
does not duplicate?  I'd rather sort it out in the known problem case.

> If not, let me have clear what you want exactly since is not clear to me from your latter mail if after the first run, AC is needed and the XO should start with AC only or battery only of both together, or doesn't matter.

Here's a specific procedure.  We are going to zero the ACR register so
that you don't have to keep track of the prior reading.

- Start with the XO in a clean working condition. ie remove all power
and battery.
- Boot the XO. Sugar or OFW either will work.
- Run on battery and allow the battery to discharge until is says its < 90%
- Connect power and let the battery charge to full.
- Reboot XO and stop at OFW.
- ok batman-start
- ok 0 bg-acr!
- Verify the ACR is really zero.
- ok bg-acr@ .bg-acr
(Should print zero)
- Remove battery
(Wait 24 hours, you can do whatever you want with the XO)
- Boot XO and stop at OFW
- ok batman-start
- ok bg-acr@ .bg-acr

That number will be the amount of capacity lost.

Richard A. Smith
One Laptop per Child

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