A number of people have posted the same issues with their Oasis.
Amazon US Customer Review
"Also, clearly the magnetized connection between the device and the case is not perfect, because I constantly, at least several times a day, will get error messages saying that the device cannot connect to the case battery. This has resulted several times in my device just dying because it is out of power."
Amazon US Customer Review
ERROR IN MY OASIS
I assume this will be swapped out when I get time to work through customer service, but there is a problem with my Oasis. It regularly flashes a warning that it has lost connection with its charging cover. Sometimes this happens when the Oasis is just sitting on the table (ie, its not being carried/moved around).
Amazon US Customer Review
I have also experienced problems with this Kindle losing connection with the battery. The work around I have come up with is to remove the battery then restart the Kindle then reinstall the battery. This happens three or four times a day.
Amazon US Customer Review
I would have given 5 stars but for fact cover not connecting properly. At least that was the error message (even though cover was charging correctly). Contacted tech support who did complete re-post. That seemed to solve problem, but after week or so got same old error message. Have requested new cover.
Amazon US Customer Review
Mine isn't charging from the charging cover (I'm returning it).
Amazon US Customer Review
I would get a sporadic error message
Charging Cover Error
The cover you have connected to your Kindle is not supported. Please connect a supported cover.
which obviously disrupted my reading experience. I paid too much money for this to up with that kind of a dumb error.
Amazon US Customer Review
When I first got my Oasis, I used it the same way I’ve always used my Voyage – cover on, flipped to the backside of the Kindle while reading. This turned out not to be ideal, because the Oasis would randomly pop up a message stating the charging cover wasn’t properly connected.
Amazon UK Customer Review
I constantly get charge cover errors and have to remove and replace the cover 2-3 times.
Amazon UK Customer Review
The Kindle Oasis would have received five stars from me had it not been for the cover/battery losing its connection with the Kindle. This happens intermittently and is an annoyance.
KBoards Thread
I've had a couple occasions where, when putting the cover on, the percentages don't show which I assume means that the cover isn't seated perfectly. Re-seating it has resolved that. A couple of times, I actually got a warning from the device that the cover wasn't seated perfectly.
KBoards Thread
I am getting the error message frequently, about the battery case not being connected.
KBoards Thread
It wouldn't stay connected to the cover and kept popping up an error message saying it was an unauthorized cover.