To maintain the current in a given electric circuit, a cell needs to expend its stored chemical energy. The cell undergoes chemical reactions internally, generating a potential difference across its terminals.

The potential difference generated by the cell, when connected to a conducting circuit element, sets charges in motion, initiating an electric current.

A potential difference is created by a battery, composed of one or more electric cells. Chemical action within the cell generates this potential difference.

Gravity plays no role in the flow of electric charges in a metallic wire. Electrons move within a conductor only in response to an electric potential difference, or voltage, along the conductor.

The analogy is the flow of water. Just as water needs a pressure difference to flow, charges in a copper wire flow only with an electric potential difference.