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Subject: Re: Re[3]: battery measurement

Re: Re[3]: battery measurement

From: Andrew Jamieson <>
Date: Thu, 19 Sep 2002 18:13:10 +1000

This is what allot of laptops do, with a circuit integrated into the battery
itself (often referred to as a 'gas guage' circuit). They precisely monitor
the current in and out of the battery over its life, often compensating the
remaining charge reported with respect to the age of the battery, and even
how 'badly' it has been treated. Maxim and Benqmark make such circuits
(such as the MAX1780). However, they are always, IMHO, quite inaccurate
after only several months of use....

The problem with doing this ourselves in the Rockbox code, is that we don't
have the accuracy of a gas gauge, and we can't predict what the user will
do. As we all know from the current measurements, if the user suddenly
decides to start skipping through tracks and browsing the menu (using extra
HDD and backlight), the time remaining will plummet ....

Also, batteries 'wear' over time. I know, for instance, that my Archos
often shuts off due to low power when there is still one bar on the meter.
This is because my batteries are over a year old, and I often leave my unit
plugged in to the wall for varying lengths of time (from days to minutes).
Put succinctly, my batteries are screwed. Allot of peoples are. Also
different people have different mAh batteries (1500, 1800, there are even
2000 you can get now). What you propose will probably work, for a few
months, for any one persons unit; if the values are tailored specifically to
their setup. I can't see us finding values that work. both accurately and
precisely, for the whole community.

However, I hate being a nay sayer, so give it a try! My nasty batteries and
I are always happy to be guinea pigs :)

Andrew Jamieson

----- Original Message -----
From: "Olivier BUTLER" <>
To: <>
Sent: Thursday, September 19, 2002 5:35 PM
Subject: RE: Re[3]: battery measurement

> The only way to get an accurate value of the remaining time is to monitor
> the current during charging and discharging ( in use ) , then calculate
> amount of energy ( kJ ) in the battery. ( Some electric shaver to that ).
> Olivier
> -----Message d'origine-----
> De : Tjerk Schuringa []
> Envoye : jeudi 19 septembre 2002 07:51
> A :
> Objet : Re[3]: battery measurement
> --- Uwe Freese <> wrote:
> > The battery status (percentage) is only calculated by the voltage of
> > the battery. So if it jumps up and down, the voltage of your battery
> > jumped up and down.
> Maybe it would be a better idea to just give the raw voltage of the
> The percentage does not give a good indication of the actual time left as
> this
> is dependent on so many factors. I used to have a cellfone (ahem, Sagem)
> that
> would give the actual voltage, and that was great. I now have a Motorola
> it
> says "40%" for days and then all of a sudden it conks out on me "LoBatt".
> T.J.
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Received on 2002-09-19

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