Stack of electric batteries including series of fluidly connected unit cells

A stack of electric batteries, comprising:

• a series of unit cells arranged in stacked layers, wherein the stacked layers are stacked successively relative to one another such that a first stacked layer and second stacked layer are opposite side outer most stacked layers with any other stacked layers therebetween,
• wherein, prior to an initial charge and an initial discharge of the unit cell, each unit cell comprises:
• a bed of metal pellets;
• and
• an air electrode,
• wherein each stacked layer of unit cells is fluidly connected such that electrolyte from the first stacked layer flows to the second stacked layer, and
• wherein the air electrode of each unit cell is connected to load bearing bus bars fixing a height of the air electrode relative to the electrolyte in that unit cell and wherein the load bearing bus bars are configured to meet mechanical support requirements for that unit cell.