RE: working age of Ni-Mh
My experience is that the lifetime of battery packs varies wildly. I have some old low-capacity NiCd packs that are 8 years old that I still fly and still have good capacity and low self-discharge rates. I've had some higher capacity NiCds that barely lasted 3 years. I've had NiMH packs that were no good even when new, and some that are still good after 5 years.
I think the best advice is to buy high quality batteries and replace them every 2 years or so. Someone who has the equipment and desire to check capacity and self-discharge rates and knows how to interpret the results can safely use them for longer. But that starts to become another hobby in itself.
I think that peak detect chargers and higher charge rates tend to shorten battery life. In my opinion, C/10 is the kindest charge method for NiCd and NiMH. I think that even C/10 may be too high for some high capacity cells. I like to charge my Eneloop NiMH packs at C/20.