I think some people are overlooking the design philosophies here regarding the Oasis.
Amazon did exactly what they wanted regarding the design factors involved. Sure, the battery is smaller and charges from the case. That's the whole idea. Granted, some may not like that idea, but that's the design Amazon chose.
The question is this (as I see it):
"Why did Amazon choose to design their new reader in this fashion?"
Let me try to answer that with these points:
1) Even with the case on, the overall design is lighter and thinner than the previous models, which gives the reader a different footprint for holding and for storing it in various places.
2) The reader becomes extremely light when the case is removed and makes for a comfortable fit in one's hands.
3) Due to point #1 [above] the reader is easily snapped off from the cover, which adds an even greater degree of comfort to the 'handling factor' when reading. When finished reading, the reader simply snaps onto [latches onto] the cover.
4) There is (for me) a certain elegance to the design that I find highly desirable when just sitting around reading.
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I realize that all these points can be refuted, if one desires to do so. Keep in mind, however, that the reasons listed above are the reasons why I enjoy reading on the Oasis - especially when lying in bed on my back.
For me, the smaller battery is a non-issue. I've never run into any problems whatsoever with it running out of juice when reading. Whenever I take the Oasis with me, the cover is part of the package and that goes with me, as well. Trying to imagine the Oasis running out of a charge is, for me, a laughable non-issee. BUT, if it ever happened, I would simply snap it onto the case.
Also, keep in mind that I own a Voyage. To me, it's not better or worse than an Oasis. It's a different kind of reader for different circumstances. The design philosophy is different. I imagine it therefore has a different kind of use.
Regarding the managing of content, I keep only Literature and literary works on the Voyage; whereas, for the Oasis I keep genre fiction on it, such as Horror and Mystery, for example.
When I go out of the house and take one of the readers with me, then it depends upon what mood I'm in for reading.
Remember, your uses may vary. Perhaps for someone here (even with the cover on), the Oasis may be too small, especially for someone with large hands. Or even for someone who is a bit uncoordinated (not that there's anything wrong with being uncoordinated).
Or perhaps you don't care for buttons? Then stay away from the Oasis! Perhaps you don't like the haptic guides on the Voyage! Then stay away from the Voyage. Again, for me, this is a non-issue. I enjoy both: Both readers are wonderfully responsive and a joy to use.
Both screens, too, are beautifully clear, with the Voyage being a smidgen darker on the letters. Hardly noticeable at all.
ENJOY!