linux-kernel - Re: [PATCH v2] Re: Battery class driver.

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Message-ID: <20061102135417.GC15184@khazad-dum.debian.net>
Date:	Thu, 2 Nov 2006 10:54:17 -0300
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	multinymous@...il.com, xavier.bestel@...e.fr, davidz@...hat.com,
	Richard Hughes <hughsient@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Dan Williams <dcbw@...hat.com>, linux-kernel@...r.kernel.org,
	devel@...top.org, sfr@...b.auug.org.au, len.brown@...el.com,
	greg@...ah.com, benh@...nel.crashing.org,
	linux-thinkpad mailing list <linux-thinkpad@...ux-thinkpad.org>,
	Pavel Machek <pavel@...e.cz>
Subject: Re: [PATCH v2] Re: Battery class driver.

On Thu, 02 Nov 2006, Jean Delvare wrote:
> On 10/31/2006, man with no name wrote:
> > In the case at hand we have mWh and mAh, which measure different
> > physical quantities. You can't convert between them unless you have
> > intimate knowledge of the battery's chemistry and condition, which we
> > don't.
> 
> You just need to know the voltage of the battery, what else?

The error goes way up when you do such calculations.  Not that most battery
hardware reports SBS Error margins right, but still...

So doing conversions is not a good idea unless it is from Ah to Coulombs or
something else like that which is an exact conversion.

In ThinkPads, you just need to compare what the various "let's calculate it"
applets say, and the output of tp_smapi (gets remanining time data directly
from the hardware) to see which one is more accurate :-)  And the difference
is often quite expressive.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh
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