According to the link below it takes a PX625 which was a mercury battery. There are a number of replacements and someone like the Small Battery Co should be able to supply one.
You can also use a hearing aid batter and then slap a rubber "O" ring to fill the space.
Or just forget about the on-board meter and use a handheld light meter. That's what I do. Truthfully, I don't have enough money or time to be changing batteries in my cameras every six months.