A friend of mine who introduced me to flying generally flies until he is .5 volts above his tx low voltage limit to avoid a dead rx battery. This hasn't failed him "yet."
No offense but your friend is headed for disaster. The transmitter voltage condition has absolutely nothing to do with the receiver voltage and should not be used as a way of guessing how much flight time your Rx pack has left in it. Get yourself a good field charger and a quality Expanded Scale Voltmeter for checking the Rx battery voltage. With a good field charger you can recharge in about 15 minutes. You can go to a 1200 mAh pack to extend the flight time but you should still invest in the mentioned items.