Question

What is the physics of how a battery works?

Answer 1

In very simple terms, there are two chemicals in a battery - one chemical wants more electrons and the other chemical wants to get rid of electrons. When a path (i.e. circuit) is completed between the two of them (the ends of a typical AA, AAA, D, etc. battery or the two posts on a 9 V battery, the electrons are free to move from one post to another. The movement of electrons is current. Different chemicals and/or configurations determine how badly the electrons want to get from one chemical to another. That drive to get from one to another is called voltage potential, and is expressed in volts. How fast the electrons travel between the two chemicals is the flow, or current, and is expressed in Amperes or Amps... for small batteries, it is usually expressed in milliamps because the current is so low. The capacity of the battery is expressed in milliampere-hours which is how many amperes can flow between the chemicals over a given amount of time until the chemicals have exchanged so many electrons that the electrons no longer have any drive to flow between the chemicals anymore.