Voltage

In electrostatic conditions, potential difference is potential-energy change divided by the charge moved between two points. One volt equals one joule per coulomb. This connects voltage with energy while allowing a field’s potential distribution to be described independently of the particular test charge used.

References: [1]

A potential value requires a reference zero, but energy transfer depends on differences. Battery terminals, resistor ends and instrument inputs each identify a pair of locations. Shifting the common reference changes assigned potentials without changing their difference or the underlying electrical process.

References: [1]

For an ohmic component under approximately unchanged conditions, current is proportional to voltage. Diodes and other devices have different current–voltage characteristics, and temperature can change measurements. Applying equal voltage to different components, or to one component under different conditions, can therefore produce different currents.

References: [2]

Sources with similar voltages can deliver different amounts of charge and total energy. Terminal voltage can also depend on operating conditions. Describing a source requires voltage together with capacity, load and losses; its volt rating alone cannot establish operating time or the total energy task it can perform.

References: [1]