How does a potato battery work? The copper (Cu) atoms attract electrons more than the zinc (Zn) atoms. If you place a strip of copper and a strip of zinc in contact with each other, many electrons pass from the zinc to the copper. As they concentrate on the copper, the electrons repel each other. When the force of repulsion between electrons and the force of attraction of electrons to the copper become equalized, the flow of electrons stops. Unfortunately it is not possible to take advantage of this behavior to produce electricity because the flow of charges stops almost immediately. On the other hand, if you bathe the two strips in a conductive solution, and connect them externally with a wire, the reactions between the electrodes and the solution continually furnish the circuit with charges. In this way, the process that produces the electrical energy continues and becomes useful.

For a conductive solution, use any electrolyte, whether it is an acid, base or salt solution. Many fruits and vegetables contain juices rich in ions and are therefore good electrical conductors.

Like any battery, a potato battery has a limited life span. The electrodes undergo chemical reactions that block the flow of electricity. The electromotive force diminishes and the battery stops working. Usually, what happens is the production of hydrogen at the copper electrode and the zinc electrode acquires deposits of oxides that act as a barrier between the metal and the electrolyte. This is referred to as the electrodes being polarized. To achieve a longer life and higher voltages and current flows, it is necessary to use electrolytes better suited for the purpose. Commercial batteries, apart from their normal electrolyte, contain chemicals with an affinity for hydrogen, which combine with the hydrogen before it can polarize the electrodes.(teachengineering.org)