Notify when battery is low at 15% (yellow coloured), and notify again when critically low at 5% (red coloured)
I'm using gnome-shell 3.28 and it notifies me one time when the battery is 5%. I believe that is sub-optimal especially when I'm not looking at the battery status, in the case of a full-screen video.
It would be better to give a first (yellow coloured) notification at low battery 15% and a second (red coloured) notification at critically low battery 5%. My Android phone does that for example.