Voltaic Piles

Alessandro Volta published a paper in 1800 describing devices that produce continual electric currents.  One version contains cells composed of zinc and copper layers separated by brine soaked fabric layers:

The fabric layers dissolve the zinc thereby pulling in zinc layer ions and copper layer electrons.  The zinc and copper layers then become oppositely charged.  Connecting the zinc and copper layers by wires produces currents.  Multiple cells can increase the currents. These devices became known as voltaic piles.