As did my Oly 35SP.... I think the number is Wein Cell MRB626, readily available on eBay at about $5 per. You get a twofer pack at this link:
When I know the camera is going to be sitting for a while, I pull the battery out and tape the air holes shut to prolong the battery life.
Correct voltage and flat voltage curve for the life of about 6-9 months.
I always have 2-3 in the drawer. Been using these for many years in my "used to use mercury 625 @1.35V" situations.
My GIII sitting right next to my monitor as I type this, with a big smile.