Each individual cell is less than 3 inches long, smaller than 1 inch in diameter and works much the same way any lithium-ion battery would in your smartphone or laptop. When the battery is charging, positively-charged lithium ions move from one electrode, called the cathode, to the other, known as the anode, through an electrolyte solution in the battery cell. That causes electrons to concentrate on the anode, at the negative side. When the battery is discharged, the reverse happens. As for those electrons, they move through circuits that are external to the battery, providing juice for toasters, hair dryers, or, in this case, thousands of homes.