Apple's AirPods ($80 at eBay) may be built primarily for use with Apple's own hardware, but they're still Bluetooth headphones at the end of the day. Because of that, AirPods work with all sorts of devices.
If you're using AirPods with an Android phone or tablet, but wish you could monitor their battery level and that of the charging case just like iOS users can, you're in luck.
I stumbled upon the free AirBattery app in the Play Store a couple of days ago.
After installing the app, open the lid on your AirPods' charging case and a popup -- similar to the one you get on-- will show up on your Android device. Battery stats for the case and each AirPod will be displayed.
Tap on the Settings cog (gear icon) to make a donation and unlock the Pro version, which removes ads and lets you customize the refresh frequency and amount of time between refreshes.
There are a couple caveats as to how battery life is reported -- primarily that an AirPod will need to be in the charging case in order for the case's battery life to be displayed.