ubuntu-phone team mailing list archive

[Selene Scriven <selene.scriven@xxxxxxxxxxxxx>]

* Matthias Apitz <guru@xxxxxxxxxxx> wrote:
> BQ.com's support said to me that I should re-calibrate the 
> battery. Which I now have done ...

It would be nice if the battery firmware (or whatever low-level 
code converts its voltage to a percent) would stop trying so hard 
to be smart.  Sometimes dumb is better.

By this, I mean it'd be nice if it would take the raw voltage, 
average out maybe ten seconds worth of values, and send that 
through a function which converts the voltage to a percent.  Set 
3.0V as 0% and 4.35V as 100%, fit the curve (at the factory) to 
the battery's discharge profile, and call it good.

This would result in some slightly odd-looking behavior, such as 
the charge going *up* after the user stops doing an intensive 
task (voltage sags under heavy load, and recovers when the load 
stops)...  and over time the "full" charge might end up being 
less than 100%.  But it would at least be completely transparent 
and avoids a whole class of bizarre and confusing bugs.

One such bug is, when the phone is modified to use a DC power 
supply instead of a battery, the charge graph goes downward even 
when the input voltage is rock-steady.  I've seen it gradually 
decline to "13%" charge at 4.35V (which should be 100%).  Because 
of this, I no longer trust the percent or the graph at all.

BTW, for an idea how voltage translates into percent, this graph 
shows the discharge profiles of a few li-ion batteries:

  http://www.lygte-info.dk/pic/Batteries2011/All18650/Capacity-0.2A.png

> Maybe it helps running a script by crond and raise alarm, if 
> battery is below 10%.

It would probably help, but due to issues like I mentioned above, 
it might still fail sometimes.

Another thing to note...  microUSB cables are notoriously easy to 
break.  You might want to try a different cable.  A failing cable 
can charge at first and then stop, if an internal connection is 
broken and only connects when the cable is torqued just so.


-- Selene