The new upcoming version of Android software shows the battery level of their Bluetooth connected devices without the need of a third-party application. This feature supported through the Android Support Library, bringing it to earlier Android versions
New version of android should allow an Android phone to display the battery level of any connected Bluetooth headphones, speakers, or other accessories. Those devices will have to be set up to share their battery information. So this feature likely won’t work with many products at first.
Rather than rely on third party applications. Either work only with a single Bluetooth device that you own or that only support a handful of devices.
Battery level indicators for connected Bluetooth devices supported on many custom ROMs and third-party OEM devices. But such a feature has notably missing from the Android Open Source Project (AOSP). Google phone on the stock firmware will not support it.
Add APIs to get remote device’s battery level
Google will add a new method in the Bluetooth Device class. It retrieves the current battery level of a connected device when called. Hence it is possible for the battery level to be shown as more informative than a simple bar.
However, it is possible that Google will introduce this API officially with the eventual release of Android 8.1. This means the new connected Bluetooth battery level reporting API won’t make its way to the first release of Android O – Android 8.0.
Google announced the third Developer Preview. It featured all of the finalized Android O APIs that developers can use to get ready for the next version of Android.