RE: retirement time
NiMh batteries do not generate a memory, as Nicd's do. Initially, NiMh batteries must be seasoned, that is to say deep cycled, so their potentional capacity can be realized. If you keep short cycling NiCd's you will induce a memory giving your battery a short run.
I have a Digipace that I bought may years ago and it served me well but today's version of battery cyclers runs rings around it, due to their ability to cycle large capacity batteries of different chemistries.
As I stated previously, you must use a meter that produces a load in order to check the state of charge. It's OK at the field, but to know its true capacity, you must use a cycler, which is impractical at the field. If you did your homework before going to the field, you can feel safe with your batteries.
Bob