An apps that show your battery level in an unique way, especially when you are gaming or watching video in full screen. You can monitor your battery level by looking at the ring surrounding your front camera.
Too bad it is not shown on Always On Display.
You can customize your ring colour based on the remaining battery percentage. Example 0% to 15% is red, 16% to 70% is Yellow and 71% to 100% is Green.
This is my ring colour when battery level is below 71%. (Green)
This is my ring colour when battery level is above 70%. (Purple)
Example of watching youtube in full screen mode with the ring.