Important: On Android 8.0 (API level 26) or above, the app may not works due to "Background execution limits" introduced in Oreo to improve battery life.
To overcome this, follow below steps:
(1) goto the "App info" screen
(2) then select "Battery > Battery optimization"
(3) set filter "All apps"
(4) locate and select Battery Widget
(5) select "Don't optimize", then "DONE"
(6) restart app to confirm is working

Graphical Battery Widget shows the exact battery level in 1x1 space, with shortcuts to Power-Summary/Display/Network/GPS/Wifi/BT Settings and 'Show Desktop' feature to shows your wallpaper/live-wallpaper in full screen.

Note:
This doesn't open, it is a Widget not an app. Add on homescreen with

Menu -> Add -> Widgets -> Battery Widget or
Apps -> Widgets -> Battery Widget

Permissions:
The permissions requested by the application can be quite intimidating, they are needed for quick access to various power settings. The application does not access/transmit device location information.

The code is open source and available on github: https://github.com/HairyRobot/BatteryWidget-gyu