I would like to know how long for is possible to store, and in wich
conditions (temperature), the out of production mercury cells 1.35Volts
PX625.

Carlo-

The reason mercury cells were outlawed, is because they are extremely hazardous
to the environment. If they end up in a land-fill, the mercury will find its
way into the water supply, which will cause illness and/or birth defects. They
must be disposed of as hazardous waste.

I believe that refrigerating a battery will slow down its self-discharge.

There is another approach you can take to use commonly available silver oxide
cells. There is an adapter that uses a semiconductor to reduce the voltage to
1.35 volts, and claims to have a resulting discharge curve almost identical to
the mercury cell. Take a look at http://www.criscam.com/mba.htm.

I have not tried this adapter myself, but plan to. I have several pieces of
photographic equipment that use the PX-625.

Fred