In most practical cases I have seen, voltage was regarded as a difference in electric potential, save the odd change of magnetic flux over time which, as a form of change, also conveys the notion of a difference.
However, from what I gather, we can ask ourselves what a sensible basal level for an electric potential might be (for example, the potential an infinite distance away from the electric charge producing it) and treat any voltage expressed in relation to it as an absolute voltage. But then we need to agree that the potential at infinity is zero. I do not know whether there are other sensible choices, but I am willing to accept that there might be.
My question is whether there are any other senses, not involving a prior agreement on a reference value, in which we could speak of an absolute voltage and, if there are, what senses would those be?