I put a [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXHDJ2&P=ML]Hobbico Voltwatch[/link] battery monitor on all my aircraft. Before and after each flight I move both TX sticks around and watch the monitor... as long as the LEDs stay lit up in the "safe" region, I'm good to fly some more... if the LEDs light up below the safe region, I recharge. I've never lost a plane or heli due to a bad RX pack with this method. However, at least two guys at my club that only use ESVs have lost their planes due to a dead pack. One guy just plain forgot to check it on his first flight... another assumed he was good for 3-4 flights before he needed to check it... and he was finally wrong. The battery monitor is always there and it's always on when you turn on your plane... and if you mount it in plain view, you'll never forget to check it.