With the latest software update (I am now on 1.0.3), one of the issues to be fixed was the "charging indicator behaviour". Looks like it was indeed the software bug. After upgrade, the indicator jumped to full 4 bars and stayed there. Beforehand, I had usually only 3 bars regardless how long it was charged.

Time will tell - I am taking the reader with me to Italy to get some mileage out of it, during transatlantic flight ...