Turtle Beach PX3 question?

The little transimitter box you get with it, how does its battery work? Does it need a constant charge? Or can you charge it via the ps3 or laptop and use it on long distance trips such as taking the train or on planes?

My plan is using the PX3 to listen to music on my iPod touch via the aux cable. But I need to know if the transmitter box needs to be plugged in to work.

Thanks

I kind of need this answer really quick so thanks for the answers :)