[brudigia]

If it helps: just had it for one week. Read one book, recharged it yesterday and I noticed an 11% drain in an hour and discovered that even though the wifi was off, the KA1 was trying to synch and there was no way to stop it, but to start it up again.

After that the synch was not there anymore.
I topped it up and did some work on the books I had loaded on it (about 1400, 203 pages). There should have been 400 hundred fewer of them, but also the ones which were not downloaded appear, thanks to the disappearance of the option for not showing them.
Anywat, just paging through them, to check for doubles between epubs and kepubs, which means turning slightly more than 200 pages, plus some activities (very few) and the battery went down to 91%.

Thus if 200 pages = 9%, 100% of battery might be good for 2000 pages. I do not believe it will ever be like that, though, because of the consumption of power for the lighting and other issues which have already been mentioned.
Even the, apparently, if well used, with no synch and no wifi, the battery should not be so bad. We shall see at the practical level, I would like to be able to read more than one book (I know it depends on the number of pages), with one charge, we'll see if I can.