V, as been discussed, is the ENERGY in joules of a unit CHARGE in coulomb. In a battery, there are many charges with the same amount of energy. Any battery will take a while before all the energized charges run out.

Q, the amount of CHARGE in coulomb, if multiplied by V will be the amount of ENERGY. This amount of charges accounts for the work or energy done in a circuit. There will always be a limited amount of charges available for work to be done by any battery.

That is, W, the energy to to the work, equals to VxQ. The unit will be joules.

I, defined as Q/t, is the rate of charges flow per unit time (1 second), when mulitply with V, is equivalent to VxQ/t which is W/t, the energy generating work per unit time. The unit will be watts. This is called the power. Power P is the rate of energy consumption. It depends on the circuit, not the source.

That is P=VxI. Compare with W=VxQ and no time (t) is involved. So the relationship of W with P is W=Pt or P=W/t. Power is the rate of generating energy or rate of doing work.