Why 2 batteries won't short like that?

enter image description here

If we connect both terminals of the same battery it would short, but not when connecting 2 different ones. How does the battery know when it's connected to itself and when it isn't?

From searching similar question I gathered that it has something to do with the salt gate, but I don't see how it solves the problem.

enter image description here

As I understand it:

  1. Electrons from Zinc flow to the copper side because Cu+ is pulling them.

Is that right? Why that happens? the sulfate-copper solution is electrically neutral, isn't it? And if it still attracts negative charge, why won't it stick to the Sodium from the salt bridge? it's closer.

  1. Without the salt bridge, the anode side will quickly get too positively charged, and the cathode will get too negatively charged as to oppose whatever happens in 1. Because the salt bridge is there, the buildup of positive and negative charges at the corresponding places gets neutralized, and what happens in 1 can continue.

Is that the answer to why 2 batteries don't short? How so?
Battery 1 anode gives electrons and neutralizes its solution with its own salt bridge, and Battery 2 cathode receives electrons and neutralized its negativity with its own salt bridge.

Why don't they short then?

Edit I think I have a breakthrough. I didn't consider the conservation of charge, I understand the importance of a closed loop now, it explains a lot.

I still got the question about the voltaic cell. Basically, what exactly starts the electron flow from anode to cathode? Both of them are electrically neutral, so what creates the flow?

  • 3
    \$\begingroup\$ Currents flow in loops. So a short circuit needs a loop. Does your 2-batteries "circuit" have a loop? In the 2nd picture I do see a loop. \$\endgroup\$ Jan 18, 2021 at 20:38
  • 1
    \$\begingroup\$ How does the battery know when it's connected to itself and when it isn't? ... it does not know anything .... your question is like how does water know when there is a hole in a bucket? \$\endgroup\$
    – jsotola
    Jan 18, 2021 at 21:25
  • 1
    \$\begingroup\$ the bottom picture shows one cell ... why are you referring to it as Battery 1 and Battery 2? ... its not even a battery unless you connect a second cell to it \$\endgroup\$
    – jsotola
    Jan 18, 2021 at 21:33
  • 1
    \$\begingroup\$ water analogy ... if bucket has a hole in the bottom, then water flows through the hole ... it's what water does ... if a cell is part of a circuit that connects positive terminal to the negative terminal, then electric current will be pushed out of one cell terminal and back into the other cell terminal ... it's what electric cells do \$\endgroup\$
    – jsotola
    Jan 18, 2021 at 22:50
  • 1
    \$\begingroup\$ The chemical reaction in the battery does not use up or create electrons, it only causes them to have pressure to flow in a certain direction. So on one end the batteries are trying to push electrons out, but with nothing nearby that wants to accept electrons it's like trying to push water into a pipe with the end plugged. On the other end, the batteries are trying to pull electrons in, but with nothing nearby willing to give up electrons, it's like trying to suck water out of a pipe with the end plugged. \$\endgroup\$
    – K H
    Jan 19, 2021 at 8:50

2 Answers 2


Current travels in a loop. Voltage is the potential to provide current with some current loop.

When we refer to a "short or short circuit", that means a shunted voltage with a very low resistance connction that forces all the current to return to the battery in that loop.

It does not mean as you have shown in your image, a "short-distance connection" which is just in series between two batteries while there is no current flowing in a loop.


The battery only has the rated voltage difference (e.g. 1.5V) between the two terminals of the battery. If you hold a battery in your hand, both of the battery terminals are insulated from everything, and thus nothing sets the voltage of either end of the battery, the battery simply sets the difference between the two terminals.

That is why they can be connected together in series or parallel without shorting, as there is no loop that would short terminals of one battery together.

Same way a 1 meter stick can be placed at the bottom of the sea or on top of a mountain, the height where the stick is does not matter, it's still a 1 meter stick, and two separate 1 meter sticks can be taped together to form a 2 meter stick.


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