Hello KeukaLite,
Welcome to CPF.
To keep your NiMh cells "vibrant," you should store them in a discharged condition. Every 30 days, subject them to a charge/discharge cycle.
Discharge them to 1.0 volts at a rate that completes the discharge in about an hour.
If you don't care about getting peak performance from your cells, you can store them about half charged.
Keep in mind that the low self discharge rate cells are a little different. We don't know enough about them yet to give you a general rule. Most of us are storing them fully charged.
Tom