If it can help others:
There is also Frans de Gruijter adapter, very well made by hand.
I recently bought one for my Pen-FT (September 2016)
If he has no stock left he will make some in a couple of days and ship it very fast,
and it has a 5 years warranty.
You then use a current, easy to find, long lasting EPX76 silver-oxide battery,
which, as the original PX625, have a steady discharge curve.
A must-read about PX625 mercury battery replacement:
It includes Frans article, which is also a must read.
His email can be found within the article PDF.