Good news for iPhone users as Apple finally announced the battery cases today for the 2018 iPhones. These new battery packs are made precisely to fit with the iPhone XS, iPhone XS Max and iPhone XR. The company promises that the extra battery will provide enough juice for the iPhone for lasting more than a day and a half. The battery comes as an accessory and is a good buy for iPhone owners willing to spend an extra $129.
The best part about this case is that you can charge the case simultaneously with your iPhone(Qi wireless charging), and you will get to know about the charging status within the Notification Center and on the lock screen. This is similar to how you check the status of Apple Watch or AirPods on your iPhone without having to check them separately.
The product listing for the iPhone XS Max battery case is mentioned as:
The Smart Battery Case is compatible with Qi-certified chargers. You can charge your iPhone and battery case simultaneously for increased talk time up to 37 hours, Internet use up to 20 hours, and even longer audio and video playback.* With the Smart Battery Case on, the intelligent battery status is displayed on the iPhone Lock screen and in Notification Center, so you know exactly how much charge you have left.
The case can be charged even faster with USB-PD compatible chargers. It also supports Lightning accessories, such as the EarPods with Lightning Connector (included with your iPhone), or the Lightning Digital AV Adapter (sold separately)