The Amazon Kindle Oasis came out in May of 2016 and one of the reasons why this e-reader costs so much is primarily due to the accompanied cover. It has a built in battery, which was designed to double the amount of reading you can do. Amazon is now selling three different Oasis cases for $89 each and comes in three different colors; Black, Merlot and Walnut.
Amazon decided to sell the charging covers separately because customers can easily damage them over time or lose them altogether. They are on the expensive side, but it sure beats having to buy another Oasis for $289.