Now I know why there isn't an application available...
The battery status API we can call in Win32/64 isn't exposed on WinRT. I'll investigate further if this is the case for Windows 8. But for Metro, aka Modern UI, I think I'm stuck.
Sent from my Windows Phone 8S by HTC using Board Express
Yep you beat me to it the api isn't supported in WP or RT.
Why then can the RT Desktop mode display the battery percentage?