With the pack reading 4.79 volts under a 300 mA load, you probably have only used up one fourth of your battery. Most 4-cell packs drop from about 5.2 to 4.8 in the first 10 minutes of use. Then they stay at 4.8 for 90 minutes, then they begin to drop again. See attached graph. You can try this: Fly two flights. Go home and sit in front of the TV and fly the plane (move the sticks around) for another 20 minutes. Then measure the voltage. I'd bet it is still at 4.8 volts. Then do another 20 minutes. etc.