No offense but the OP did not ask for a way to do this in the OS. He asked for "a good way to see remaining battery life in Windows RT". A live tile would be in Windows RT and would absolutely qualify. Kricke's reply was helpful. Astounding that most of a year later MS still haven't fixed this. The app store is a massive fail.
I was looking for this as well but now I realize that real estate on the Start/Metro screen for tiles is a premium.
I no longer want to take up a tile just displaying this information.
To me, the quickest way from just about anyplace or any app, is to simply swipe in the charms bar from the right
and on the bottom is a clock with a pic of the battery power remaining. I now use this as my go to.
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