Aurra - I don't think charging them twice in a day hurts them, just as long as they have enough time to cool. I don't run my NiCads mor than once per day.. nomatter what, but they usually get a couple hours to rest between uses...
NiMah like the second go around though...
I don't know much about rates... I always charge my packs at the same rate per pack... but i change for diff. capacitys..