Mercury PX625 batteries are obsolete.
My friend Martin asked me if I could mod his light meter, so it could be powered by normal AAA batteries.
The required schematic is very simple, a mercury battery gives an exact 1.35V, so the 2 batteries from the light meter together, give 2.7V. I just use a suitable small regulator, in this setup :
To make it small enough, I built it all on a tiny footprint adapter, which fits into the battery compartiment.
Add the 2.7V regulator to it :
Add the 2 SMD capacitors (can you spot them ?)
And added a clip to it, so it can slide over the battery contact (when I bend the battery contact upwards)
Added some isolation, the whole thing plugs into the battery compartiment like this :
Now just add a 3xAA battery holder and... ready ! It works well.
The light indicator works !