nicad/nimhs can be tricke charged and 1/10C rate, if you want your batteres to last as long as possible then you should trickle charge them between events for 14 hours at that rate (they dont have to be flat before hand), this balances out all the individual cells, the only reason I can see for discharing is to find out the battereis true capacity and if you wish you can do this after a trickle charge, then you can charge them normally.