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sansa battery life

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AutobahnSHO:
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Sorry, got mesmerized by your avatar pic.  ;D

Rockmenot:
Just after reading this thread. I was alarmed to notice that when in rockbox, once the battery meter says abotu 40% it just ticks down in about 20 mins rather than the 5 hours it says i have left.
I shouldnt be too alarmed it seems. I havn't done a full battery bench yet but the fact it drained VERY fast once it hit ~40% worried me.

scarfy:
I have the same problem.

I only have the % listed on my WPS, since I the runtime estimate too unwieldy.

My Sansa goes to about 40% or so and I know it will shut off soon there after. I still get about 10 or so hours out of my player before hand...

I'm guessing that the threshold voltage for the low battery has been set too high somewhere in the source. Either that or my battery is knackered. Although I have only had my Sansa for about 9 months, and always fully charge and discharge it.

Anything I could do to help find out what's wrong..? Battery bench? Play around with the voltage setting somewhere?

scarfy:

--- Quote from: Rockmenot on December 18, 2007, 09:23:14 AM ---Just after reading this thread. I was alarmed to notice that when in rockbox, once the battery meter says abotu 40% it just ticks down in about 20 mins rather than the 5 hours it says i have left.
I shouldnt be too alarmed it seems. I havn't done a full battery bench yet but the fact it drained VERY fast once it hit ~40% worried me.

--- End quote ---

I can confirm this; it just happened to me. I'm going to update my Rockbox tonight after I've charged up my Sansa and let you know how I get on*

(* - I'm away from Christmas, so it'll be a while before I comment again...)

P.Opus:
Quote from: Rockmenot on December 18, 2007, 09:23:14 AM

Just after reading this thread. I was alarmed to notice that when in rockbox, once the battery meter says abotu 40% it just ticks down in about 20 mins rather than the 5 hours it says i have left.
I shouldnt be too alarmed it seems. I havn't done a full battery bench yet but the fact it drained VERY fast once it hit ~40% worried me.


I can confirm this; it just happened to me. I'm going to update my Rockbox tonight after I've charged up my Sansa and let you know how I get on*



All,  This is "normal".  If you look at the Wiki regarding the Sansa battery benchmarks, you will see that the battery discharge rate for the Sansa is fairly flat with two exceptions.

Battery discharge rate from a full charge is fairly rapid, and then flattens out quite a bit, until about 40%, at which point the discharge of the battery is accelerated.

Since any "percentage" or "time remaining" charge is simply based on the voltage readings at the given time, this "%" and "Time Remaining" reading is highly inaccurate due to the sharp discharge curve at the beginning and end of the discharge cycle.

Even the original firmware does not attempt to give a time remaining function as there is no real "mathematical" way to figure it out, and simply basing it on output voltage would not yield accurate results.

On my discharge tests, I've had the battery take almost two hours to go from 50% to 40%.  Yet 40% to shutdown is less than an hour.

Plan on approx. 10 to 12 hours per charge (charge only using original firmware), and once you get down to about 42% you know you are going to have to plug in soon.

If you are looking for more battery time, run the device in original firmware, as that firmware is optimized for power, where as Rockbox is not.

Rockbox is better than it was, but 10 to 12 hours of "normal" use (use of backlight, volume level) is about what you are going to get.  If you turn off all the EQ settings and simply run it continuous with no use of the backlight, you may be able to coax an hour or two more out of it, but the battery remaining level will always be inaccurate.

What would be nice is if we could change the range of the battery remaining feature so that we can only include the flat portions of the discharge curves.  This would compensate for the sharp discharge curve at the  end of the cycle.  I'd set the "empty" percentage to be at approx 3.4 volts., as this is very close to the low power shutdown for the device.

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