NiMH are self discharging so always charge before use.
I have been using this type of battery for three years, in the most power hungry of cameras,the Minolta D7. during this time I have never discharged the batteries before recharge. I have taken well over 25,000 photos during this time and I am still using my original four sets of batteries. They do not suffer from the memory effect, so don't waste your time discharging them.
The batteries and chargers I use are Ansmann & Maha, maybe a little expensive but well worth the extra.