P.D and Voltage

[Music Man]

Are potential difference and voltage different?

Say you have a small 9v battery compared to a car battery.
One can create a small current for a long period of time while the other
can create a very large current for a small period.
Even though they have the same voltage,is the difference that one has
more ionised particles on both sides(- +) than the other.
Is voltage defined by how much a material is ionised?

For instance if I rub my shoes on the floor and touch some metal there is a
spark
when I Earth.If the metal is not ionised how do extra electrons pass
themselves over
from me to metal,thus earthing?

Thanks