[Tinyos-help] Battery voltage curves - Estimating battery lifetime from Voltage

[Benjamin Madore]

I would like to say that this is the most eloquent explanation I have seen
for the question of battery monitoring on motes.

On Mon, April 30, 2007 11:31 am, Steve McKown said:
> Assuming you aren't periodically recharging your battery, you can use four
> variables to give you a very rough idea of battery condition: chemistry,
> temperature, current draw, and battery voltage.  If you can consider the
> first two fixed and always sample voltage at a known current draw (perhaps
> cpu running but all peripherals off/sleep), then you can create a low
> battery
> indicator by only reading the voltage and comparing it to a constant, with
> hysteresis.
>
> When people begin wanting to look at the battery condition closer, very
> often
> the cost to do so exceeds the benefit.  Ultimately, we came to the
> realization that the best time to save power is when there is lots of it,
> since you get a multiplying effect.  Consider that 10% less energy draw over
> the operational range of a battery is a better deal, energy-wise, than
> saving
> 30%, but only during the last quarter of the battery life.  Because battery
> life is so important in our application, we chose to give up some
> functionality to sip power all the time, looking at battery capacity only to
> generate a "service me" indication.  The end result was simpler and more
> efficient hardware and software.  Of course, this line of reasoning may not
> apply for your application...
>
> All the best,
> Steve
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