If I have understood you. You say the radio is about a month old and you have flown it twice before. How many times have you charged it? What did your battery checker tell you at the field?

Even if the charger had been left on permanently then you should not have damaged your batteries to that extent (providing you normally use a trickle charger). If you constantly use the quick charger you might want to 'cycle' it a couple of times with the trickle charger.

Fully draining the battery is not really recommended.

How many flights you can get depends on the capacity of your battery. A 700mAh or 800mAh battery will last a fair while with a four or five servo plane. (if I don't have my battery checker I limit myself to about four or five flights to be on the safe side).

It sound like you have another problem to me. Were you flying from the same field? Were both transmitters on at the same time? Did you try your transmitter on your friends plane? If both transmitters are know to be serviceable then the problem lies with your plane. Was the engine running? What have you done with your receiver antenna? Can you try a different crystal in the receiver?

Don't want to throw you off the scent but it could be many things other than the battery.

Let us know what you find.