Your battery contacts did look corroded in that picture.
I found the ISO accuracy not that accurate on mine. If you suspect so then shoot a roll of slide film. Shoot a series at 1/3 stop ISO brackets and keep notes. The look at your developed slides to see if the set ISO was best or if you were getting accuracy at ISO settings over or under the actual film rating. You can then apply this factor to you favorite film (if color negative etc.)
They are pretty cool cameras and I think there is a site or a blog that is devoted to them. There is also some info on the web about battery options as well. The camera does have a battery check button.
