If you press it once and wait, the watch will display battery information, the date and the weather following the digital time. (pocket-lint.com)
The app itself also comes with battery information, shortcuts to things like WiFi and Bluetooth settings, and it even gives you charts to show more detailed battery activity. (androidauthority.com)
While this app is excellent to get battery information on your lock screen and also on live tiles very accurately. (windowslatest.com)