linux-kernel - Re: [PATCH v2 1/4] power: supply: core: Introduce one property to present the battery internal resistance

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Date:   Wed, 26 Sep 2018 14:45:10 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        yuanjiang.yu@...soc.com, Mark Brown <broonie@...nel.org>,
        Craig Tatlor <ctatlor97@...il.com>
Subject: Re: [PATCH v2 1/4] power: supply: core: Introduce one property to
 present the battery internal resistance

Hi,

On Wed, Sep 26, 2018 at 04:30:39PM +0800, Baolin Wang wrote:
> Hi Linus,
> 
> On 26 September 2018 at 16:00, Linus Walleij <linus.walleij@...aro.org> wrote:
> > On Wed, Sep 26, 2018 at 4:59 AM Baolin Wang <baolin.wang@...aro.org> wrote:
> >
> >> Introduce one property to present the battery internal resistance for battery
> >> information.
> >>
> >> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
> >> ---
> >> Changes from v1:
> >>  - New patch in v2.
> >
> > I'm a bit confused by the physics in this patch.
> >
> > The internal resistance of a battery is not a constant in its life cycle,
> > this varies over the age of the battery, and the reason I thing is
> > chemical residuals accumulating on the anode and cathode inside
> > the battery and the energy storage medium aging. (Plus/minus my
> > ignorance about how batteries actually work.)
> 
> Yes, you are right. The internal resistance can be affected by
> temperature or battery age or other factors. But our solution just
> uses one constant internal resistance to calculate OCV value to look
> up the capacity table when system boots on, in this case we do not
> need one more accuracy OCV, since we will calculate the battery
> capacity in future. So we just introduce one estimation constant
> internal resistance.
> 
> >
> > AFAIK the fact that the internal resistance varies is of high
> > importance for people developing algorithms of battery capacity
> > and longevity. Such that some (hardware) capacity monitors go
> > to great lengths to measure with high precision the current
> > internal resistance of the battery for their algorithms.
> >
> > Sorry for making things more complex, but should it be named
> > "factory-internal-resistance-micro-ohms" or
> > "typical-internal-resistance-micro-ohms"?
> 
> I am fine with this change. If Sebastian also agree with this change,
> I will fix. Thanks for your reviewing and comments.

Ack.

FWIW for proper battery status you need to collect battery specific
statistics, that is the reason fuel gauge chip providers recommend to
combine the chip with the battery cells into a "smart battery".

-- Sebastian

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