Yours is a pretty routine setup (same one I flew last year, BTW). I could get in about 4 ten minute flights before the voltage on the RX pack told me it was time to go home or field charge.

If you don't have one, invest in an Expanded Scale Voltmeter (ESV) which measures the battery voltage while under a typical 300mA load.

On a fresh charge, my 4.8 volt pack will actually measure around 5.4 volts. After each flight, it will measure fewer volts. Once it gets to around 4.5 or 4.4 volts, that's when I call it quits. It will actually stay at 4.8 volts for a fairly long period then drops rapidly.

It's pretty good practice to replace your NiCD packs once every 3 years. This year I went up to an 1100mA NiCD pack. A couple of weeks ago we put in 8 full flights and still had 4.5 volts remaining. That was nearly an hour and a half of flight time!