Electronics: Voltage

 Voltage is the element that helps current flow from point A to point B and it gives an electromotive force (emf) which points from the negative side of the battery to the positive side. Here's a lithium ion battery and its interior, with an LED light for reference.

As you can see the Magnesium Dioxide is the cathode and the Magnesium Trioxide with the OH- is the anode (correct me if I'm wrong). Reactions will release electrons, when there's the zinc anode reacting with a Hydroxide particle, it produces Zinc Hydroxide as a byproduct and releases electrons aggregating in the anode. These electrons, as a result, want to travel to the cathode, because of the magnetic forces. Light happens when the proton releases valence electrons and heat. The electrons move from the anode to the cathode at the speed of light, and the voltage can be measured as the change of potential energy to the charge, or ΔU/q, Potential energy is measured in Joules between 2 electrons. When the potential energy increases, the smaller charges get ever so closer to one another. 

The ground is the negative term of the battery. Each conductor will have a slight voltage drop, but this would be negligible in calculations, since the value is so small. So far we figured out that 1 volt is the equivalent to 1 Joule per Coulomb, and power is in Joules, so 1 Joule is the work taken to move X Coulomb of electricity over a period of time, in short, power measures speed. So power is the rate of work over time. P = dW/dt which implies that it equals VdQ/dt since work = potential difference * charge. 

The ground reference for voltage and measurements can indicate and change the voltage at certain points.

We can also refer to the DC volt pump in a water pump analogy. The current can represent water flow and the water can represent the charge in coulombs. The + sign can add voltage positive from the ground, and the - sign subtracts from ground.