"Memory" is a myth. When NiCDs first came out they were used primarily in lab conditions where they were discharged to the exact voltage level every time and they developed a "memory". If they were then tested, their voltage would drop off quickly after they reached that point, but our situation, and the technolgy of the cells is different today and it's simply not true. But like most myths, it doesn't die easily.

I generally leave my packs in whatever condition they were in when I left the field, then give them a good "overnight" charge before I go to fly (at least 14 hours or so). Or I use a Quick Peak charger to charge them on the way to the field. As long as you don't exceed 1C (1 times the rated mAH of the pack) you won't have any trouble. I have packs that are 4 to 5 years old and still test at 90% of their rated capacity.

Your transmitter pack will usually last at least 8 to 10 flights. The receiver packs usually won't get you more than 4 flights before the voltage is too low to fly safely. You should check the voltage with an ESV (like the one Raideron linked to) after the 3rd flight (minimum), and EVERY flight after that.

I won't fly if my pack gets down to 5.0 volts, but having a Quick Peak field charger lets me charge packs whenever I want, so I can fly all day. A pack discharged to 5.0 volts can be recharged with a Quick Peak charger in about 20 to 30 minutes at 1C.

You can pick up an inexpensive Quick Peak charger for around $35, then go to Radio Shack and buy a car "cigarrette" lighter adapter and charge directly off your car battery.

Later on, you can buy a couple of 6 cell RC car packs, wire them in series, and use them on your 12 volt airplane starter. You can charge that at the field too.

Have fun.
Dennis-