The Pixel 2 and Pixel 2 XL flagships are able to show battery levels of Bluetooth devices, as suggested by the teardowns of the SystemUI and framework-res APKs performed by XDA Developers. The relevant code found in the files indicates that the functionality is either live or essentially ready to go live through a server-side switch and will allow the upcoming Android-powered smartphones to feature battery level indicators for accessories paired with them via Bluetooth. The indicators themselves are likely to be placed in the notification tray and always be visible by default, as is the case with similar implementations of the feature on handsets from Samsung, LG, and a number of other original equipment manufacturers.
The image that can be seen below is a cropped version of one of Google's Pixel 2 XL promotional renders and shows how the device will display the battery level of the Pixel Buds once it detects the earbuds and offers to connect with them, though it's possible that the smartphone will handle third-party accessories in a different manner, especially if they don't bear the "Made For Google" certification. The fact that the SystemUI APK contains references to the feature is a clear indicator that the battery status icon will be part of either the navigation bar, status bar, or both. The source managed to identify the same code strings in the Settings package, suggesting that users will be able to check the battery levels from the "Bluetooth" section of the system Settings app and possibly opt to turn off the indicators which are understood to be enabled by default. The analyzed files were made for Android 8.0 Oreo and the original Pixel and Pixel XL should also be able to take advantage of them once they're distributed by the Alphabet-owned company. The Pixel 2 series will presumably support the functionality out of the box, though Google has yet to officially confirm that.
As Google developed a native solution for battery level reporting on Bluetooth devices, the need for third-party apps offering the same feature will presumably cease to exist among the majority of owners of the company's Android smartphones. With the service being an integral part of the Android operating system, it may also be more efficient or work in a more reliable manner than the existing solutions.