[roger64]

Thanks you all for your help, explanations and improvements.

I understand now that I can use a wall charger with my Kobo Glo equally with Nickel, KSM or Koreader, the difference between them being only about reporting.

I did the same test with KSM 07 (battery level 96%) and I got some more information than with Koreader because there is a refresh button* which allows the user to update the information about the battery without having to reboot:
1. - when plugging the charger, a tap on refresh tells me that the battery is now charging (the previous status was discharging)
2. - when unplugging the charger after about 45 minutes, a tap on refresh tells me that the battery capacity reached again 100% (maybe this level was reached before, I don't know)

* KSM 07 - tools/checkbatteryautorefresh.sh

Edit: I will resume the same test with Koreader later on, when the level of my battery will be much more depleted (20, 30% left?) so as to make unprobable any "wonky jump" which could put in doubt its results for this reason.