The cases, which are only available in white or black colours, look like regular phone cases - except they have a large bump on the back for the extra battery. This design is very similar to the Smart Battery Cases that Apple developed for iPhone models prior to the iPhone 7. In fact, Apple has not offered a Smart Battery Case option for the iPhone since the iPhone 7, likely due to the wireless charging feature on newer phones.
There has also never been a battery case for the larger iPhone models. These new battery packs, however, work with both the large and standard new iPhone models. They also charge wirelessly, or via Lightning, and faster charging via USB-PD compatible chargers. Once charged, they wirelessly deliver the bonus juice directly to your iPhone. You will even see a battery life bar on your lock screen and in the notification bar.
The amount of extra battery you will get depends on which version on the iPhone you are using and how you are using it. The iPhone XS case, for instance, will offer an added 33 hours of calling time, 21 hours of surfing the internet, and 25 hours of video playback. The iPhone XS Max case, on the other hand, promises to deliver 37 hours of call time, 20 hours of internet, and 27 hours of video playback.
The iPhone XR case will improve the battery life of the iPhone XR to 39 hours of call time, 22 hours of internet, and 27 hours of video playback.
If any of these interests you, the new Apple Smart Battery Cases are available now for $129. You can buy them at Apple.