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Calculating how much time we have left... - Technical Blog of Richard Hughes

Richard Hughes
Date: 2007-02-06 16:47
Subject: Calculating how much time we have left...
Security: Public
GNOME Power Manager sometimes really gets the time remaining wrong. It doesn't help that the ACPI BIOS sometimes misrepresents the data values, the units, or just gives bogus readings, but we should at least try to be accurate.

So I've been playing with a historical correction-matrix approach, at the moment targeted to the li-ion discharge curve. Initial results are very encouraging, and appear to be much more accurate than relying on the embedded controller data for my dual core laptop and my old iBook. Factoring in battery temperature would likely give an even more accurate answer.

And then I stumbled on this patent.

It appears to patent a method of reading the battery total energy and dividing it by the discharge rate, and then correcting it with a chemistry profile and specific historical correction matrix. Ahh...

This seems fairly obvious calculation to me, and I would hardly call it an invention (it's a formula with method), but I do not want to put a feature into g-p-m that is clearly patented. The patent would also likely explain the lack of documentation available online, and why all of the battery discharge chips are very closed source.

So, where do I go from here? I've not released any code, but I would appreciate your advice about what to do.
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User: deviant_
Date: 2007-02-06 22:07 (UTC)
Subject: (no subject)
Oh, and the obvious (though I haven't read the patent, so it still may be covered) workaround: instead of using a profile of the battery chemistry, use a matrix of previous discharge rate intervals indexed by the charge at the time and the actual average discharge rate during that interval.

That is, build a table based on the physical properties, not the chemical ones.

And my way is better, of course -- if you do it right, you should get *better* accurate results without having to have info about a particular battery's chemistry, or even having more general "oh, it's lithion ion" type data.
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