I think I know what the problem was - for 'convenience' I had put no books on the internal memory, and everything on an SD-card; requiring constant card-access when using the reader. Now that I moved my books to the internal memory, probably combined with the 'first recharge' effect, I have not had to recharge again. Still on my 2nd recharge, still all bars full
I've also just downloaded my first borrowed books from netlibrary.com, which works like a charm. No problems left, just enjoyment - I was finally able to do some studying, reading and annotating a text, out on the balcony, in bright sunlight.