I am going through the DC book and find the analogy with water flow a very good one, but there is one thing I find a little confusing:

I assumed that the poles of a battery are isolated from each other, because on the one side you will have a surplus of electrons and on the other side you will have a deficit, thus creating a voltage drop between the poles.

However, in section 1.4 (Voltage and Current), the water analogy goes on to say that there must be a continuous flow back to the reservoir, and there is an illustration of a pump pushing the water (which are the electrons in the analogy) back to the reservoir to form a closed loop.

This is confusing, as it seems to suggest that electrons must be flowing inside the battery as well, but I thought this not to be the case.

Please can you help to clarify this for me.

 

Yes, the electrons flow inside the battery. Else they would come from nowhere and go to nowhere...right?
They flow in the battery and the internal resistance of the battery becomes included in the total resistance of the circuit, especially with very small batteries.

 

Yes, the electrons flow inside the battery. Else they would come from nowhere and go to nowhere...right?

From the description about static electricity, with which the book starts, I pictured the poles of the battery in a similar way; the negative end having a surplus of electrons and the positive end having a deficit, so that if you put a wire between the two, the electrons follow the flow until the balance is restored and the battery is spent.

 

Batteries are more like a chemical motor. They don't have all the electrons piled up and waiting like a capacitor, they reach an equilibrium between electromotive potential in the chemicals and charge "ready to go". After you release some of the potential energy by letting some electrons flow, the chemical process resumes and moves some more electrons to the end terminals.

 

Great. Thanks for clarifying that! (y)