[kubuntu] Screen flickering on low battery level

Hi everybody,
I'm an old Debian user and wanted to try Ubuntu, so i've recently installed Kubuntu 16.04 LTS (with KDE Plasma 5) on my Asus laptop.

Some days ago I tried to install nVidia drivers but nothing came up, so I reverted (or I guess so) to the "original" situation. Everything works fine (actually I don't neet my card, integrated graphics works fine for me now). I've only one issue... when battery is low (20% and lower) my screen starts flickering bad when opening "new graphic elements"... What can it be? When battery is above 20% (or so) I have no flickering at all, same when plugged to AC (even if battery level is low)

The command

glxinfo|egrep "OpenGL vendor|OpenGL renderer*"

OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) Haswell Mobile