Hate to open up an old thread but since I had this same issue and found my own work around I thought I would post it. I found people on the net saying they had good luck with 675 hearing aid batteries so I picked up two packs from CVS on sale, buy one get one free. Since the diameter of the new batteries was much smaller than the original I simply cut two pieces of heavy paper one about 3/16 of an inch and another that was about 3/8 I rolled the smaller piece tight, dropped it into the compartment then rolled the larger and dropped it inside the first. A little playing with it got a good snug fit. I enlarged the hole on the back of the battery cover to allow better air circulation the followed the instructions from http://www.graphic-fusion.com/lunapro.htm to recalibrate it to the higher voltage.
I hope this helps anyone else looking for a good, cheap, easy way to keep their light meter functioning.
As an interesting aside. The 625 batteries in my Luna Pro were put in in 1973 before I moved to Nova Scotia. They have never leaked and still go to the check mark.
Newer batteries in other equipment are long since dead.
I have been told that the life of these batteries depended on the purity of the raw materials received by the manufacturer.
675 hearing aid batteries are 1.4v and should not require calibration.
You can get 8 675 Walgreen's brand for $7.99 and with two #9 rubber o-rings($2) to fit around the 675, you are in business. I just put an older Luna Pro(says Germany(West)) back in service with this method and the meter checks out perfectly.-Dick