Batteries are made up of three main components: a ANODE (-), a CATHODE (+) and between them, a ELECTROLYTE. Electrons move between the anode and the cathode through the external circuit, while ions are transported through the electrolyte to balance the charge. Different metal combinations require different electrolytes that must efficiently allow the movement of ions while not corroding the anode and cathode. 

Reference: Conceptual diagram of the global communications platform