Right, so this is probably a pretty noob question, but I'm really interested so anyway...

Suppose I disconnected the negative terminal on my cars lead-acid battery. Instead I grounded the frame of the car to a good ground. The voltage difference is now 12V again and my car should work, right? The current would flow from the positive terminal to ground. Would the battery still work, ie. would the chemical reaction still take place, since there is nothing connected to the negative terminal?

What if I did it the other way around and connected an outside 12V DC source to the car, but left the negative terminal connected to the car with no other ground.

I hope my question makes sense haha. I don't know enough about batteries and electrical engineering to understand what would happen

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    \$\begingroup\$ Current flows in a loop, it is not clear (to me) where your loop is. \$\endgroup\$ – Tyler Nov 6 '18 at 2:46
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    \$\begingroup\$ "ground to a good ground". What? Be explicit. Draw a diagram or risk being forever misunderstood. \$\endgroup\$ – Bort Nov 6 '18 at 3:26
  • \$\begingroup\$ imgur.com/a/CbvIB9z \$\endgroup\$ – harbl Nov 6 '18 at 12:47
  • \$\begingroup\$ This is what I was thinking of. The potential difference between the positive and the other ground is the same as between the positive and negative terminals. Thanks. \$\endgroup\$ – harbl Nov 6 '18 at 12:48

If you leave either terminal of the battery unconnected, no current will flow from it. For current to flow there must be a complete loop, or circuit, and the resistance along the path of the loop and the voltage(pressure) applied will determine how much current will flow.

Note that in electrical and electronics it is not uncommon for things to be referred to as ground that are not actually grounded, and are simply a dedicated return path for current. For this reason, the new convention in electrical is to refer to things that are directly connected to ground up to the point the connection diverges(IE a ground rod pounded directly into conductive earth, the wire attached to it up to the first enclosure in which it splits are ground. Anything past that point in green or bare copper is "bonding")

Your question seems to stem partly from the idea that the "ground" on your car is related in some way to the "ground" that is the earth.

The electrons that flow out of the battery must be replaced by the electrons flowing into it. A battery does not supply you with electrons, it provides you with the emf(voltage/pressure) to make them flow. The electrons are already present in the materials the electrons will flow through(conductors). If you think of a copper wire as a pipe for electrons, you must think of it as a pipe that is already completely full of them.

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  • \$\begingroup\$ Thank you very much for your explanation. Well I think that I understand that there is a potential difference of 12V between the positive battery terminal and everything connected to it, and between the “ground” which is the chassis of the car that is connected to the negative terminal of the battery. Hence current will flow. \$\endgroup\$ – harbl Nov 6 '18 at 12:36
  • \$\begingroup\$ What if I create a voltage difference between the positive terminal and something outside of our battery. There would be a voltage difference, so would current flow? \$\endgroup\$ – harbl Nov 6 '18 at 12:43

Ground is a relative source, and can be thought of as a "sea of charge." The neutral terminal of your car battery is not necessarily the same charge as the Earth ground. In fact, the charge of the Earth varies by location and can even change depending on soil conditions etc. This variance is small but has to be considered in some applications. So the positive terminal of your battery is only positive in reference to it's negative terminal. It is possible for it to even be a lower charge density than actual "Earth". As for your question, because there is no way for charge to flow from the Earth into the negative battery terminal, no charge will flow, meaning there is no current.

Think about the physics of a battery, the potential is generally caused by atoms being ionized. The atoms in the negative side of the battery have taken an electron from the atoms in the positive side. To be balanced, all the "negative" atoms would like to give their electron back to the positive side atoms, when they have a path for this, a current will flow. Note that the entire battery "system" is in a balanced state. However, if the charge flow went from the positive of the battery to the Earth, or a different battery, then the system would no longer be in balance for both batteries. Creating this unbalance requires work, thus it will not happen spontaneously. Fun fact, an ideal battery will very slowly drain when the positive is connected to Earth (or to anything) as the air will carry a tiny amount of charge from on terminal to the other.

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  • \$\begingroup\$ Thank you. But what would happen if I found a suitable ground or negative terminal that has a potential difference to my positive terminal? \$\endgroup\$ – harbl Nov 6 '18 at 12:28
  • \$\begingroup\$ I have added further explanation to my answer in the second paragraph. \$\endgroup\$ – Burritos Nov 6 '18 at 17:36

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