Are they NIMH?
A freezer is good for storage of NIMH.
Aging of batteries is a chemical process, and freezing them pretty well stops the process, so that there will be little ageing, if any while in the freezer.
The life is usually considered to be a number of charge / discharge cycles, but storing them fully charged does place stress on the dielectric, so store them with only a small charge in the freezer, and don't worry about them.
Its basically the same reason that we stored film in the freezer, the chemical process was halted, so film degraded very slowly and could last dozens of years.
If you only use your camera occasionally, just freeze two of the batteries.