iPhone4 how to find out if the power cable is plugged in?

Question

I would like to know if my app is running with an external power cable attached. Is it possible to find out this state at runtime?

An extra question: would this be able

Answer 1

I had to include the line,

[[UIDevice currentDevice] setBatteryMonitoringEnabled:YES];

or else batteryState only returns UIDeviceBatteryStateUnknown. Perhaps this became necessary since this question was initially asked and answered. I found the tip here: Determine accurate iPhone battery level.