NOT from me (RNinMunich)! I just edited it to delete a previous comment of mine!
NiMH batteries should not be discharged fully although it wont do them too mcuh harm if this happens. They are not very good for high load applications and tend to deteriorate quickly if put under any load.
To charge up these batteries use this formula.
These batteries should not be placed under any 'fast charges' as they deteriorate too quickly for the amount of amps put through them.
NiMH batteries seem very popular these days as it is a new technology and a lighter weight battery than others. The battery is also recyclable, and eco-friendly, but all this doesn't make it a practical battery to use. it is recommended due to the deterioration rate of this battery to stick with NiCad's for higher current applications.
These batteries should be kept charged up. A charge for half the time of a normal charge every two weeks will be sufficient to keep the battery in its best condition.