A jailbreak tweak allows it
BatteryLevelAE is a Cydia package which adds Siri the ability to tell how much battery time is left on your iPhone
Siri is a multi-purpose information assistant but with extra tweaks available to jailbroken devices, it becomes an almost infinite source of information.
The BatteryLevelAE is a package available through Cydia, the alternative to the official App Store, that uses Siri to provide accurate battery life statistics like how many time left if you use Wifi, 3G and so on. Do you only need to have a jailbroken iPhone 4S with iOS 5 installed and 0.99$ to spend.
According to CultofMac:
If you try the app, let us know.
NEWS SOURCE: http://www.cultofmac.com/155850/how...fo-about-your-iphones-battery-life-jailbreak/
Our thanks to 'Kaos2K' for another news story!