https://phys.org/news/2019-01-apple-battery-case-latest-iphones.html

The new cases come in black or white and are lined inside with a soft microfiber.

According to Apple's own tests, the designated talk time for the iPhone XS, XS Max and XR cases are up to 33, 37 and 39 hours, respectively. Internet longevity for the three phones are up to 21, 20 and 22 hours. And video playback is rated at up to 25, 25 and 27 hours.