For a little while.  Do you know the mAh rating of your flight box battery?  Figure that you'll need about 1.2 to 1.5mAh out of that for every one that goes into your flight pack.

The flight box battery is rated at 7.2 AH

You'll get maybe two charges out of it.  Three if the battery works as rated, you have a really efficient charger, and your plane doesn't draw the pack down too much each flight.  I don't know if gel-cell batteries can stand routine deep discharge or not (someone chime in here!!!), but it certainly won't help the life of the thing.