ORIGINAL: Red B.
I have found that at most I can get 10 fifteen minutes flight out of a freshly charged Rx battery pack. Usually I call it a day after eight 15 minutes flights.
I find that I get about the same on a stock 600mAh battery using four standard servos.
I always check the battery with a load meter after the sixth flight.
Usually I try to replace the 600mAh batteries with higher capacity ones. I then take the 600mAh batteries and either place them into planes that I do not fly as often in a given day ( I haul out at least TWO planes to the field on each trip ), or put in two of them on a plane.