[Gta04-owner] Battery charge profile

NeilBrown neilb at suse.de
Sun Feb 26 04:45:18 CET 2012

On Sun, 26 Feb 2012 00:10:17 +0100 Christoph Mair <christoph.mair at gmail.com>

> On Sat, Feb 25, 2012 at 11:41 PM,  <d0m1n1k at gmx.net> wrote:
> > as far as i know the gta04 can run on usb, at least if there isn't too much
> > activity.
> > wouldn't that be the preferred way once the battery is charged?
> > are the components connected in a way that the software can switch between
> > power sources?
> This behavior should work out of the box (at least it does work with
> my device): If I connect the USB cable the power drawn from the
> "battery" (my laboratory power supply) drops to zero.

You power supply presumably has different current/voltage characteristics to
a real battery.

There are various components in the GTA04 which are connected directly to the
battery (VBAT), so the voltage they see will be exactly the same as the
voltage the battery see.

If the BCI (battery charge interface) provides a higher voltage than the
battery provides, it will charge the battery, as well as drive the various
If the BCI provides a lower voltage, the battery will drive the various
components and will be drained.
I don't think it is realistically possible for the BCI to provide exactly the
same voltage.

So the battery will always either charge or drain - unless you pull it out.

What voltage does you power supply provide Chris?  I suspect it is a little
bit higher than the BCI provides, and it has diode protection against a
reverse current so it does see any current drain.

If we wanted to disconnect the battery (which would not be a common use case
with a phone I would think) we would need a dedicated switch to do that.  The
twl4030 power management chip doesn't provide that function.
> > Am 25.02.2012 22:14, schrieb NeilBrown:
> >
> > Does anyone know much about battery charging?
> > My inclination is that I would rather it didn't get quite that low.  90% is
> > about the minimum I feel comfortable with, 95% is probably better.
> >
> > I can program that voltage cut-off level to anything from 3.75V to 4.1V
> > (approximately) in 23.4mV steps.
> > 4.1V corresponds to a charge of about 94%.
> >
> > So to my question:  What is a good profile for a battery to encourage long
> > life, or to balance that sensibly with usefulness?
> One thing I know is that Li-Ion batteries age faster if they are fully
> charged. From a battery perspective it would probably be the best to
> keep the charge somewhere between 35% and 70%. Of course this is not
> really useful for a mobile device. I would probably target the 4.1V
> cutoff voltage.

That brings up the interesting question of when to stop charging.
According to the docs, it should stop when the charging current drops to 80mA.
However the battery sees the current go all the way down to below 1mA before
charging stops.
I wonder what is going on.

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