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Electric Potential and Charge Flow:
Electric potential is a location dependent quantity that describes the amount of electric potential energy per charge possessed by a charged object at a given location. In order for charge to flow from one location to another location, there must be a difference in electric potential between the two locations. If there is a difference in electric potential between the two locations, then charge will spontaneously move from the location of high potential to low potential.
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The Role of a Battery:
The role of a battery (or cell) in an electric circuit is to supply energy to the circuit by doing work upon the charge to move it from the low energy terminal to the high energy terminal. By moving charge to high energy, the battery (or cell) is establishing a difference in electric potential across the two ends of the external circuit. With this difference in electric potential established, charge will spontaneously flow through the external circuit.
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In a sense, circuits are all about energy. Energy is introduced into the circuit by the battery. The battery acts as a charge pump in a circuit, moving charge between terminals so as to supply an electric potential difference across the two ends of a circuit. It serves an analogous role as the water pump in a water circuit. The battery moves the charge from low energy to high energy much like a water pump moves water from low energy to high energy. Both processes require the input of energy to the system. If the battery is the energy input location of a circuit, then the energy output is the light bulb. In this sense, circuits are all about energy - energy in at the battery and energy out at the light bulb.
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