I am with the above poster. The battery should match voltage and have at least the same or higher current rating(mAh or Ah).
I think the other site was try to reffer to the difference between battery voltage and charger voltage.
The laptop has as voltage regulator that changes the incoming voltage to whatever the battery needs. Now in some cases it may have a wider range(Wider range would allow you to use higher or lower voltage), but its not worth finding out the hard way.