An electrochemical cell is a device that either generates electrical energy from chemical reactions in a so called galvanic or voltaic cell, or induces chemical reactions (electrolysis) by applying external electrical energy in an electrolytic cell.

Both galvanic and electrolytic cells can be thought of as having two half-cells: consisting of separate oxidation and reduction reactions.

When one or more electrochemical cells are connected in parallel or series they make a battery. Primary battery consists of single-use galvanic cells. Rechargeable batteries are built from secondary cells that use reversible reactions and can operate as galvanic cells (while providing energy) or electrolytic cells (while charging).

A galvanic cell (voltaic cell), named after Luigi Galvani (Alessandro Volta), is an electrochemical cell that generates electrical energy from spontaneous redox reactions.

A wire connects two different metals (e.g. zinc and copper). Each metal is in a separate solution; often the aqueous sulphate or nitrate forms of the metal, however more generally metal salts and water which conduct current. A salt bridge or porous membrane connects the two solutions, keeping electric neutrality and the avoidance of charge accumulation. The metal's differences in oxidation/reduction potential drive the reaction until equilibrium.

Key features:

Galvanic cells consists of two half-cells. Each half-cell consists of an electrode and an electrolyte (both half-cells may use the same or different electrolytes).^{[citation needed]}

The chemical reactions in the cell involve the electrolyte, electrodes, and/or an external substance (fuel cells may use hydrogen gas as a reactant). In a full electrochemical cell, species from one half-cell lose electrons (oxidation) to their electrode while species from the other half-cell gain electrons (reduction) from their electrode.^{[citation needed]}