Old clip+ battery: recompile with half CPU frequency ?

[g.orlandini]

Hi all,

I've a Sansa Clip+ (6 yrs old) which I use mostly for podcast with very low CPU demand (OGG, bitrate 16Kb/s) while I hear music in my "new" FIIO M3k.

Battery in Clip+ is lasting less and less (50% original time):

If I recompile Rockbox with half normal CPU Frequency (19,2 MHz) and half boost CPU frequency (96 MHz) do you think I could save some battery time and still have a usable player (no problem for small lag in starting), hearing podcast or simple music mp3 ?

Thanks for your help

[saratoga]

I doubt you'd save much. You'll be running at a steady 38 MHz stock so about as low as it gets.

I'd replace the battery if it's failed.

[g.orlandini]

So you don't see a lot of battery saving (>10% runtime) if CPU is working @19,2 MHz instead of 38,4 MHz ?
Battery is still usable but with a limited runtime (10 hrs aprox.).  I guess in a year it will be much less.

Thanks for your advice

PS I searched this file firmware/target/arm/as3525/clock-target.h and it seems 38,4 MHz is already the lowest frequency, no 19,2 MHz available.

[Bilgus]

I did a lot of testing on the clip+ I actually took and added a current shunt inline with the battery
when I was looking to optimize the runtime of the device

Its been a long time but IIRC the biggest driver of power use was the display
the voltage tweaks to the CPU that caused problems for so long were within measurement error

best things to extend the battery life:
backlight exemptions,
codecs that take less RAM and are lightweight for decoding by the CPU
leaving audio processing off

for better battery longevity
don't fully charge or fully discharge the battery liion doesn't like either extreme

[g.orlandini]

You're right, thanks for your battery saving's advices. I'll try to save my clip+ as much as possible.

[g.orlandini]

I noted the old battery was charging at maximum Voltage (4.18 V) even when starting with a low battery level (30-40%). I guess battery life should be improved with a slower charging current and more important with a lower voltage (of course, at a cost of a longer charging time and a small loss in total battery capacity).

I've found in "/rockbox/firmware/target/arm/as3525/powermgmt-target.h" #define BATT_CHG_V and #define BATT_CHG_I which I guess control battery charging setting.
Is it OK to change default values (CHG_V_4_20V - CHG_I_140MA) with those (CHG_V_4_10V - CHG_I_70MA) written below to lower battery charging to 4,1 V - 70 mA?

#define BATT_CHG_V          CHG_V_4_10V
#define BATT_CHG_I          CHG_I_70MA

Any other settings to control clip+ battery charge to 4,1 V - 70 mA in a safe way?

Thanks to share your opinion (I'm a newbie and I prefer to ask experts)

[saratoga]

Lowering the battery charge voltage won't slow charging, it'll just prevent you from charging to 100%.  You can reduce charging speed by changing the current.

[g.orlandini]

Thanks for your answer.

I guess that If I write #define BATT_CHG_V          CHG_V_4_10V in "/rockbox/firmware/target/arm/as3525/powermgmt-target.h" then max charging voltage is 4.1 Volts.

I guess that if I write #define BATT_CHG_I          CHG_I_70MA in "/rockbox/firmware/target/arm/as3525/powermgmt-target.h" then max charging current is 70 mA.

My question as a newbie is:

Are there other files to change other than "/rockbox/firmware/target/arm/as3525/powermgmt-target.h" in order to charge battery @ 4.1V - 70 mA?

Thanks to all
 

[g.orlandini]

I've recompiled Rockbox with:

#define BATT_CHG_V          CHG_V_4_05V
#define BATT_CHG_I          CHG_I_55MA

and so far it looks OK (charging limit voltage @ 4,05V and limit current @ 55mA).

Thanks