until this gets fixed
http://en.wikipedia.org/wiki/Patent_encumbrance_of_large_automotive_NiMH_batteriesI wouldn't waste my time or money on ni-mh.
you don't need to charge them all the way up or all the way down, it doesn't matter if you use CC or CV, provided you stay below 90% SOC.
i don't think there's any reason not to charge them to 100%, other than the fact that they absorb any overcharge by recombination of hydrogen and oxygen.
as the cells age there may be an imbalance, and the cells will vent oxygen, why? IIRC they make the negative plate bigger so it can't vent hydrogen
they do make ni-mh cells designed for float charge, just like they did ni-cd cells back in the 1990's (you will find these in surplus fire escape lights)
but the smaller cells will be destroyed by cheap chargers with no temperature correction.