Best Battery for Olympus Pen FT?

I just got another used Olympus Pen FT. I am using an LR 44 standard button battery. I get over-exposure in bright light and under exposure in dim light. Thoughts? Thanks in advance.

The camera used a mercury 625 cell so anything that creates a different/not as constant current, assuming the battery you use works in the camera, is going to require some amount of compensation The Wein zinc-air cell PX625 is as close to a replacement as it gets today, short of having the camera modified by a repairer to operate appropriately with something different, like what you are doing.

Thanks so very much for your help, Greg M !!!