The Electric Potential of Charged Particles

Electric potential energy is a property of the electric field itself, not of the particle we have there. Just like my gravitational potential energy depends on my mass and the mass of the earth and it depends on where I am relative to the earth. The force between positive and negative charges or in other words the electric potential energy will depend upon the distance between the source and the test charges. So you can do it either way it just depends on what your reference is what you're looking at.