I understand that a 9V battery will produce an electrical potential difference/voltage of 9v across the positive and negative terminal, with the positive terminal having the higher potential by definition.
I am aware that the actual electric potential at the positive terminal may not be 9V or 0V for the negative terminal but the difference in the electric potential is 9v.
Wikipedia tells me that the electric potential of a point is the amount of energy needed to move a unit positive charge from a reference point, usually infinity, to that point. I do not understand how this relates to circuits.
My question is really what is meant by the actual electric potential at the terminals of each battery and is it possible to measure?