All those little bikes took a small 6 volt battery. A lot of the smaller Jap bikes took the same size. If you look on Ebay you will find the owners manuals forsale and a lot of other parts and new battery's. You should not need a battery to get it running. I have had a number of these little bikes over the years. Infact I think there are pictures of my bikes on here somewhere.
good luck with your project.