Your laptop is dual core so when it says 50% it is using 100% of one processor. Which is what your PC has, one processor.

As far as on your PC you could use ctrl-alt-del to open the process viewer and set the priority of the task lower. However this will impact performance resulting in an even slower render.

It doesn't appear that batch rendering would resolve this issue.

I believe that it is normal for the CPU to operate at 100% when rendering. But don't take my word for it. As far as your other issues with the render crashing it could be a memory issue, not related to the CPU.