[Gta04-owner] bq27000-battery: battery is not calibrated! ignoring capacity values
edorfaus at xepher.net
Sun Feb 3 22:47:03 CET 2013
On 02/03/2013 05:18 PM, Bob Ham wrote:
> I'm wondering if anybody here can provide some authoritative information
I'm not an authority on the subject, but I figured I could provide some
details on my (limited) understanding of the problem, just so we're all
on the same page.
> What precisely is it that needs calibration?
> Why does reporting the charge depend on this calibration?
The OpenMoko battery contains a bit more circuitry than most batteries,
including a bq27000 chip. This chip measures and keeps track of several
things about the battery, including the current going into or out of the
battery, and this lets it know the charge level of the battery. The
GTA0x then communicates with this chip via the third contact to display
information about the battery, such as max and current charge level, and
the mA currents we see on the home screen.
Keeping this chip inside the battery instead of in the GTA0x is because
it allows you to have more than one battery, and/or use the battery in
more than one device, while still maintaining accurate and up-to-date
That bq27000 chip is what appears to needs calibration, presumably to
know the characteristics of the actual battery it is in, I'm guessing it
in particular it needs to know the max and min charge levels that the
battery will hold, to be able to calculate things like how full the
battery is or how long it is until it's empty.
While it apparently knows the values the battery was designed for, those
values will change as the battery wears down (which, for LiIon
batteries, includes simple time passed), and it needs to know the
actual, measured, values to have any accuracy.
> How is the calibration performed, and by what? Is there a problem with
> the GTA04's hardware, or with the kernel, or is this expected behaviour?
I assume the calibration is performed by the chip itself, when the
device/user follows some kind of procedure to calibrate it, meaning that
this is (kind of) expected behavior.
The problem is that, since we haven't seen the datasheet or any other
relevant information, we don't actually know what that calibration
procedure is supposed to be.
I guessed that the discharge-recharge cycle would do it based on some
information I read about some completely different battery (for a Mac
IIRC) that apparently had something similar in it, but it is a pure
guess that it would use the same (or an equivalent) chip, or that the
procedure would be the same.
On 02/03/2013 05:18 PM, Bob Ham wrote:
> Unfortunately, charging and discharging my battery has not helped. I
> have had it charge/discharge continuously for weeks and I still get the
> errors. This includes complete discharges followed by a spell in the
> GTA01 to charge the battery to a level where it can power the GTA04 for
> a full boot. I still get the same kernel error messages.
Yeah, that's something I probably didn't make completely clear in my
previous mail, that I disabled powermanagement and stuff so that it
would discharge completely (power off the device due to lack of power,
not due to software noticing it had little left), and then left it
overnight or so after that. I see you did the same anyway though.
I used the GTA04 to recharge it though, and made sure to recharge it
completely, and IIRC left it charging a while longer just to make sure.
(Or was that in the initial charge before the deep discharge... I don't
I only did this procedure once, not multiple times. I was already
worried before I did it, because I know that LiIon batteries don't like
being completely discharged. (For longevity, they actually prefer being
around 50% charged, and to be fairly cold.)
As I mentioned, it didn't immediately start to work for me either, but
after a few minutes, it started providing information.
So, for all I know, it might have been a coincidence that it started
working for me after I did that.
Like you, I sure would like to see some kind of official information
about this, preferably including the documentation on calibration.
I kind of think it would be better if the factory calibrated the
batteries before they shipped them, but I guess that's impractical for
several reasons. Not the least of which would be that it might be a
while before they're sold, which can change their characteristics.
By the way, as I mentioned in that mail, my (brand-new, for me at least)
battery already had a quite a bit lower charge_full than
charge_full_design, so using charge_full_design is likely to be
inaccurate for many.
Another point to consider is that, if this is changed so that it's not
really visible to the user when the battery isn't calibrated, they're
unlikely to look for information about it - and thus unlikely to get
their batteries calibrated, which I assume would leave them with much
less accurate battery information. So we might want to show it somehow -
a different color on the battery indicator? An exclamation mark next to
it? A message on the home screen? I don't know what would be best, or if
such information would even be desired by anyone other than me, but I
tend to favor providing such information whenever possible, because I
know I would prefer getting it.
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