You won't get a great starting current through your booster cables. Contrary to popular belief, that's not how it works. I think once you have a good battery installed completemy, these issues will go away.
If you still have a slow crank issue after "installing" a good battery, then you may have a sheared decompression pin. Although going solely on what you have typed above, I do not believe this is the issue.
If you still have a slow crank issue after "installing" a good battery, then you may have a sheared decompression pin. Although going solely on what you have typed above, I do not believe this is the issue.