Amazon.com Inc. unveiled the Kindle Oasis — the eighth generation of its popular e-reading device — hoping book lovers will be willing to pay more in exchange for a sleek design and months of reading without charging the battery.

At $289, the device costs more than three times as much as the most affordable Kindle available today. The new model features a protective case that doubles as an extra battery, providing as much as nine weeks of reading without a new charge.

Amazon sees electronic readers as a key strategy to selling more books since digital volumes cost less and are easier to distribute than printed copies. Amazon began as an online book store and now sells 4.4 million electronic book titles, including 1.1 million added last year. It also sells $10-a-month subscriptions to Kindle Unlimited, which gives users access to more than 1 million e-book titles and thousands of audiobooks.

At 4.6 ounces and 0.14 inch at its thinnest point, the Kindle Oasis is 20 percent lighter and 30 percent thinner than earlier versions. The beveled design — thicker along one side — makes it feel even lighter because the center of gravity is closer to the readers’ hand.

The Kindle debuted in 2007 as Amazon’s first consumer gadget.