ACtually, my wife has left the cord into my JR Quattro (that I use as a buddy box) and it drained the freshly charged (only flown once on the day) 700 mah battery in just a couple of hours. We returned to fly hers again, and the battery was dead, and the tx had shut itself down.

So I can be a problem. Don't forget and leave it plugged in, or it will definitely shorten your student's day.

BTW, the Spektrum DX7 powers up the same way when a buddy cord is connected. The futaba to JR cord is a different animal all together.