Sansa clip without any juice in battery

[Yak39_9]

Hello,

This is my first message and this unfortunately already an SOS.

Last week, i have found out my old sansa clip v1 from 2008 with, of course, no more battery, with native sansa firmware*. After a week end, i reached the conclusion that i could use it in my car wish has an usb port for external usb stick.
At home, plugged on my smartphone charger, it was working like a charm !!!

Then i decided to install rockbox on it. I restarted it and could see the wonderful logo of rockbox.  Let me remind you that my sansa clip has no more battery; i mean absolutely no juice. I was searching through the menu to change the language, when suddenly sansa clip switched off (~20 seconds after rebooting).
I restarted it with the power button, but again, after 20 seconds, sansa clip switched off.
Absolutely no way to maintain it switched on.

1st solution : Staying with my sansa under rockbox firmware >> Is ther a special setting I could activate to fix my problem ?
2nd solution : Migrating back to native Sansa firmware >> So I tried to remove the bootloader with rockbox utility, but after 20 seconds sansa clip is automatically ejected and disappear from windows explorer.

Please help

*as there is no more battery, only solution to record new settings (radio station, language ...) was to activate the timer (10 minutes); without this trick, brutal unplugging device made all my settings lost at the next boot

[Yak39_9]

Holding left while powering on, make a reboot into the Sandisk firmware.
I didn't know that. So I can now update to sansa firmware 

What about fixing the automatic low battery shutdown in Rockbox ?
Someone had a similar behaviour of powering down after 22 seconds. At the end of this post, he managed to fix it, by adding a line code

#define "NO_LOW_BATTERY_SHUTDOWN"

Could anyone guide me how to patch it. I am not sure if a newbie can do it

Thanks