What goes on, exactly, inside those AAA batteries powering your LED flashlight? The short answer is: Chemistry. Chemical reactions can encourage electrons to flow out from one terminal and back to the other, doing some useful work along the way. Meanwhile, inside the battery, positive ions, also known as electron-holes, are changing places. Eventually the chemical reactions run down, and the battery stops delivering power. If it is a rechargeable type, you can force the electrons and the positive ions to go back where they started, ready to run again.