They several different brands of NIMH batteries and the storage and case of each.
Seems not all to be stored the same way.
So I can't honestly say how I would do it.
I just pulled out a 3300mah pack that has been laying on the shelf for a year
and charged it and the boy ran it in his torment without issue.
From another site.
Storing your cells
NiCd and NiMH cells can be safely stored for very long periods of time if you follow these procedures:
Always remove a NiCd or NiMH battery pack from the device that uses it before storing the pack.
Occasionally discharge your packs down to 0.9V/cell or, if possible, individually down to zero volts per cell (anything below 0.8V is essentially completely discharged). A charged pack that is allowed to self-discharge is subject to large crystal formation and voltage depression when used again.
Do not exceed 85°F. (30°C.) during storage. Keeping the temperature a lot lower is preferable, but do not go below 32°F. (0°C.). A lot of NiCd/NiMH battery pack users have very successfully stored their packs in the refrigerator or freezer but we feel that the need for air-tight wrapping and the inconvenience when thawing out the packs isn't worth the trouble. Lower temperatures slow down the self-discharge rate of the cells but we recommend cycling the cells every few weeks. Balance the possible benefits of long-term storage (without worrying about self-discharge) against any possible inconvenience when thawing out the packs and choose the storage method that works for you. You'll be fine either way.
Store the cells in an air-tight container or other packaging to prevent condensation if the cells need to come up to room temperature after storage (and before using them). Some cells can be stored (and used) at very low temperatures, down to -40°F. (-40°C.). Check the data sheet of the manufacturer of your cells to be sure.
To use the cells after they've been stored, perform a slow 0.1C-rate charge and 1C-rate discharge before charging again normally and using them. If the cells have not been conditioned every 3-4 weeks during storage, you may need to cycle them this way up to 3-4 times before the cells regain their rated capacity.
You'll often see advice to store NiMH cells partially charged. But, we've been storing all of our NiMH packs discharged to 0.9V/cell between uses and haven't damaged any cells or measured any loss in capacity or reduced voltage under load. In addition, none of the major cell manufacturers that discuss storage of their NiMH cells say that a partial charge is needed. In fact, most state that they can be stored discharged.
The only sure reason we know of for storing NiMH packs partially charged is that certain chargers won't start if the voltage of the cells is below a certain level. Since NiMH cells self-discharge faster than NiCd cells, there's a chance that these chargers might not charge a NiMH pack that hasn't been used or cycled in a while. We don't recommend buying one of these chargers as they prevent you from slowly charging over-discharged packs or packs that haven't been used in a long time.
But, with all of the conflicting information available on the Web, we decided to do a test. After charging and 2-stage discharging three different 10-cell NiMH battery packs to 0.9V/cell (cycled 3 times), we stored all three packs for 8 weeks at room temperature. After 8 weeks had elapsed, the following pack voltages (no load) were measured; 11.71V, 11.79V, 12.32V. No individual cell had dropped below 1.0V.
Based on these tests, cell manufacturer recommendations and our experience over the years using various NiMH battery packs here at CamLight Systems (and always discharging them to 0.9V/cell before storage), we have the following recommendations:
If you're storing a NiMH battery pack for a month or less, discharge it to 0.9V/cell. No need to partially charge it before storing it.
If you're storing a NiMH battery pack for longer than a month and you own a charger that will not start if the voltage of the cells has dropped too far, and you don't want to cycle the pack every month or so, discharge the pack to 0.9V/cell and partially charge it (about 10%). When you're ready to use the pack again, you will probably need to cycle it at least once to restore its capacity and voltage under load.
If you're storing a NiMH battery pack for longer than a month and you have a charger that won't prevent you from charging when the pack is below a certain voltage, just cycle the packs every 4 weeks or so. This helps to condition the cells and makes it easier to bring the packs back up to their rated capacity and voltage under load when you're ready to use them.