Fully discharging any battery isn't good for it. NiCd had the particular problem of "memory" developing though, so going through a full discharge cycle was necessary to prevent the memory forming. It wasn't good for the battery, but it was better than letting the memory develop.
I'm not aware of NiMH developing a memory, so that wouldn't be a good thing to do with NiMH either. I always tried to avoid full discharge of my NiMH batteries and always got a pretty long life out of them.
Really the full discharge cycle is an artifact of the needs of one particular chemistry (NiCd) that became something that "everybody knows" you should do long after it became counterproductive.
There are two types of discharge states - typically "fully discharge" implies within the application the battery was designed, not completely dead. For example, a car battery is fully charged at 12.6v, but discharged at 11.2 (or somewhere around there). There is still lots of capacity left, but dead for the use of cranking over an engine. NiMH typically has a very fast self discharge rate - letting these dip well below the operational capacity level will be much more detrimental than just letting your drill die after prolonged use.
NiMH has memory too, but not as bad as NiCd. We always suggested allowing NiMH to fully discharge time to time, but we never suggested keeping a phone on its base constantly.
Both these types of batteries need to be primed properly - full discharge/recharge the first few cycles. (Not sure about the new pre-charged NiMH, like Eneloop)
Memory builds faster when left in a discharged state.
Cadex machines can be used to reverse memory, to an extent.
I'm speaking from memory from 6 years ago. Hopefully I didn't mess up too much =P
There is occasionally a need to do a full or nearly full discharge on Li-Ion batteries in order to recalibrate the state-of-charge indicator if the embedded controller gets confused, or if the battery is nearing the end of its usable life and has significantly diminished capacity.
But in general, deep discharges are bad for any electrochemical cell, and should only be done to prevent or forestall something worse.
NiMH cells shouldn't be "topped off" when they're nearly full, but that doesn't mean they should be fully drained before charging.
Fully discharging any battery isn't good for it. NiCd had the particular problem of "memory" developing though, so going through a full discharge cycle was necessary to prevent the memory forming. It wasn't good for the battery, but it was better than letting the memory develop.
I'm not aware of NiMH developing a memory, so that wouldn't be a good thing to do with NiMH either. I always tried to avoid full discharge of my NiMH batteries and always got a pretty long life out of them.
Really the full discharge cycle is an artifact of the needs of one particular chemistry (NiCd) that became something that "everybody knows" you should do long after it became counterproductive.