Never On Sunday

Eileene wants to attend NYC Resistor’s class on batteries, if she can talk herself into the drive deep into Brooklyn tomorrow night. I think it should be interesting. Run by hackers—“hackers” in the original sense of people who cobble together doohickeys—its proposed topic list includes practical concerns that I couldn’t answer myself: how to choose the right battery for the job, why rechargeable batteries stop recharging, and what you can do to maximize their life. But mostly I would like to know why batteries work in the first place.

I can get most of it. Two phenomena are in tension with one another: the tendency for electric charges to seek equilibrium and the differing valences of two metals. Two metals in contact with an acidic solution have different degrees of affinity for their electrons. As a result, the metal with the greater affinity tugs electrons out of the solution, which in turn tugs them free of the metal with lesser affinity in order to restore its neutral charge. Okay, so far so good. This creates a different tension, because both metals become ionized; the first metal, now negatively ionized, seeks to shuck electrons in order to return to its original neutral charge while the second metal seeks to replace the electrons it lost. Okay, I can grasp that principle in itself, but I don’t see where the circuit comes in. Why doesn’t the initial exchange of electrons happen right up to the point where it balances the increasing and contrary impetus towards neutral charge, and stop? Why is there an ongoing circuit at all?

On a related matter, given that a circuit exists at all in this setup, why should it stop operating? Yes, the second law of thermodynamics prohibits energy from nowhere. But given that an ongoing exchange of energy can happen in the first place, and not a simple rush to equilibrium, what, mechanically, makes that exchange stop?

One can look up the answers to these questions on the web. Unfortunately, the answers are not presented in a fashion that I find readily digestible. I need to ask follow-up questions, to establish certainly the meaning of jargon and to handle in greater detail the steps in the process that aren’t quite sinking in. For that, one needs a live teacher. Answering an unresolved question of long standing, if little immediate import, strikes me as a fine way to spend an evening, driving or no.