There won't be a Modern UI App that will be able to read the Power Management API as it isn't exposed in WinRT. All of the Modern UI Apps are "sandboxed" to prevent instability to the system and other Apps. The only way for Modern UI Apps to "talk" to each other are through pre-defined "Contracts"
The main Contracts Are:
•Share Contract - can automatically share content to and from any other app that also supports the contract.
•Search Contract - You can use the search charm and search across different applications such as – Bing, Twitter, etc.
•Picker Contract - allows you to get files, data, pictures from one app to another app.
•Play To Contract - You can help your users play digital media to connected DLNA devices from within your app