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I was sent here by the folks on the physics stack exchange as they thought my question was more chemistry-related, but I am only a 10th grader and don't have a very strong chemistry background, so please be patient if I am not very proficient in expressing my question.

I was trying to figure out why parallel connected batteries don't add voltages, and the exceedingly common answer was that batteries act as sources of fixed potentials, not fixed fields. So my next step was to figure how they maintained a fixed potential - I discovered this answer which explains how batteries maintain a constant potential difference.

So what I understood was the field created by the batteries grows in strength as more charges are spewed out of the cathode. When this field becomes strong enough, it stops the redox reactions occurring in the battery. This causes the potential difference to become constant as there is no more charge accumulation.

I have my doubts about this explanation - I thought potential difference had nothing to do with how many charges there were present, but rather that the battery added some amount of energy into electrons coming out of the cathode which created a potential difference that was used to do work in a circuit.

At this point I am confused about how a potential difference is created by a battery - is my past understanding correct or does charge density truly create voltage? If charge density does create voltage, what is the point of adding energy to electrons inside a battery (if the chemical reactions in a battery even "add" energy to the electrons)?

If charge density does indeed create voltage, how would that explain stuff like voltage drops accross resistance?

Note: I want to know what happens at the atomic level, not analogies.

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    $\begingroup$ Delete whatever you have been reading on the internet and random websites about electrochemistry, including Q&A in physics from your mind. They can easily drive any sane mind crazy from rambling "answers". I understand that you are in grade 10 and your curiousity is appreciated. Only read stuff which has been written by reliable authors, i.e., published books or research papers for concepts. Can you access journals? There is a beautiful article, "Potentially Confusing: Potentials in Electrochemistry" DOI: 10.1021/acsenergylett.0c02443. There are so many potentials. $\endgroup$
    – AChem
    Mar 3 at 8:15
  • $\begingroup$ @AChem Perhaps later you might add a short answer that tells how Volta, long before the discoveries by Dalton, Davy, Faraday, etc., devised his condenser electroscope and used it to find the polarity of charges on the poles of his voltaic piles. ;-) $\endgroup$
    – Ed V
    Mar 3 at 13:38
  • $\begingroup$ @EdV, So far no student or teacher has ever questioned the obvious. $\endgroup$
    – AChem
    Mar 3 at 15:42
  • $\begingroup$ The battery (for simple example think of galvanic cell) starts operating through spontaneous chemical reactions happening at electrodes. The electrons move between the electrodes depending upon the feasibility of reaction. The driving force here is provided from chemical work which is apparently non-conservative.This process continues until an equilibrium is reached , irrespective of the connected external circuit. $\endgroup$
    – An_Elephant
    Mar 4 at 13:07
  • $\begingroup$ @An_Elephant, If I remove the word "apparently" in your text, that is, if I write "from chemical work that is not conservative" instead of "from chemical work that is apparently not conservative", is there anything wrong? $\endgroup$
    – HEMMI
    Mar 4 at 22:34

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I think it's important that you understand what a battery is and how it works from your question.

A battery is a portable galvanic cell.

It depends on the type of galvanic cell, but I'll give you an example of a Zinc-Copper battery. I don't understand what you mean by the addition of energy to electrons.

On one half cell is the anode. This is the site of oxidation. In this one, you have zinc ions in solution and the anode is made of zinc metal.

On the other half cell you have the cathode. This is the site of reduction. You have copper ions in solution and a copper cathode.

Linking these two half cells, you have two circuits: the internal circuit and the external circuit.

Internal circuit contains a salt in solution. Let's say KNO3. External circuit is just wires. Zinc is of course the stronger reductant, so it is oxidised like so:

Zn(s) --> Zn2+(aq) + 2e- That makes a charge difference, so the internal circuit spews respective ions (NO3- in this case) to balance the charge in solution.

The electrons flow through the wire to the cathode. They come into contact with Cu2+ ions and make solid copper metal. Also, potassium ions are shot into solution to balance charge.

Also, in regards to potential difference and charge density. Voltage is related to how many electrons pass through the wire in a span of time. Voltage is also the potential difference. Stronger oxidants tend to have a larger E degree value than stronger reductants. Below hydrogen, they have negative values. So, the larger the distance between reductant and oxidant, the greater the potential difference.

I don't get what you mean by charge density. The charge on either side of the cell remains the same. In the wire, it makes more sense to talk about rate of oxidation and electron flow than charge density.

At least, that's what my textbook says.

Hopefully that answers your question.

You should do more research and find more reliable sources.

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    $\begingroup$ Rather, a battery(1) can be, among other meanings, a set of connected batteries(2), where a battery(2) is a portable galvanic cell. For the case of car batteries of 6 or 12 cells, here the battery is not a portable cell and their cells are not really portable. These are fruits of not keeping meaning of words. $\endgroup$
    – Poutnik
    Mar 5 at 8:44
  • $\begingroup$ Intrinsic Voltage is not determined by current flow altho it can affect operating voltage. An electrolyte carries current it is not spewing ions, it may or not be nonreactive. In you example it is imperative to prevent copper ions from contacting the Zn metal. To maintain a constant voltage the cell must have a low internal resistance and the change in activities of the anode and cathode reaction chemicals must be kept as small as possible over the useful life. Parallel connection simply increases the amount of chemicals in the cell with no effect on the voltage. $\endgroup$
    – jimchmst
    Apr 6 at 3:10

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