Unless some one else on here has a magical way of getting that screw out. You will at minimum have to replace the shaft. But if you can get maybe 6 or 7 threads of a screw into the shaft. You can cut a screw to size and use loctite for a temporary fix. You maybe able to get away with less...
maxamps.com, you can get battery packs from 4 amps to 12 amps, and batteries at 7.4 volts to 22.2 volts packs. I had to deal with their customer service recently. They are great. I would give them a try.
Nick