What we know is freely available. There's gaps in our knowledge though. Studies sometimes just don't happen or can't isolate real effects easily.
...and hype loves gaps, so keep that in mind.
Generally manic symptoms are seen with nootropics.
I think it is hard to say how effective they really are for test taking. They can't make you any smarter, but they can calm you down and help you focus.
You don't have a battery, but yeah, there can be issues. This one people describe altered behavior as well as trouble during withdrawal.