[wave solder]

I have been lucky on both of my Sun voyager and my Sun IPX machines in that the deceased coin cell in old age had expanded and cracked the top of the plastic module so all I had to do was remove the broken bits of plastic and with a tiny screwdriver prise out the old coincell, solder two pieces of tinned copper wire to the two stubs of metal left behind. To these two pieces of metal I then soldered on the coin cell holder (observing polarity) then glued it in place on top of the module.