What are you worried about? It shouldn't damage your PowerBook/iBook to try it.
If it's an Apple battery or from a reliable aftermarket manufacturer like Newer Tech, it'll probably work if it truly is new-in-box as you say (not doubting you, but the party that sold it - I would view such a claim with healthy suspicion). It may not have a long life, as there's a life span to the chemistry inside those batteries; but might work for a while at least at some level.
If it's a no-name or Chinese aftermarket knockoff, it still might work, just don't ever let the charge get below about 25%. In my experience, those don't reliably report their charge level and tend not to recover from being fully discharged.
It'll either be a brick or it won't be. Take your shot.