Indicates the current battery charge level as a value between 0.0 and 1.0.
On return, level is a number representing the system's battery charge level scaled to a value between 0.0 and 1.0. A value of 0 means the battery, which is a BatteryManager object, is empty and the system is about to be suspended. A value of 1.0 means the battery is full. A value of 1.0 is also returned if the implementation isn't able to determine the battery charge level or if the system is not battery-powered.