RE: LIFE battery charging in the plane question
You can't really compare a high internal resistance cell like a AA Eneloop with an A123 M1 cell for weight. If you use digital servos of anything past 50 in-oz, you should not use AA cells. The 2700 A NiMH cells aren't much better. You should compare a Sanyo CP 2400 5 cell pack to a 2S A123 pack which have about the same specs for BOTH current and capacity. The A123 wins big time. Also note that NiMH cells dump in cold weather. I originally went with Sanyo 4/5 FAUP 1950 cells. They were fine until it got cold - 50F. I was completely happy with Sanyo RC 2400 packs when they were available some 10~15 years ago. I went to A123 because I kept buying "new" NiCD packs that had set around a warehouse for years. As Red said, NiCD cells are dead after 7 years (shelf life) if you have used them or not.
I have a concern about cell redundancy. If one cell fails in a 2S pack, you are probably coming down. A 4 or 5 cell pack can tolerate a dead cell and keep right on going. I used to put diodes across the cells (ancient idea) in case one of the cells "opens". But 1 A123 cell plus a diode is 3.6 - 0.7 = 2.9 volts optimistically and at least Futaba digital servos die at 3.2 volts. I have a VoltMagic thing set up to go yellow at about 50% capacity remaining at which time I BALANCE charge the pack at 2.3A - about 30 min.
1) you should loosely mount your batteries in foam or several layers of foam tape
2) you should not over charge or discharge