Ok in this thread I asked about the potential difference between two separate batteries. My thought was, that if a voltage of a battery is all about potential difference between the two terminals, then theoretically, there could be a potential difference across the negative terminals of 2 separate batteries, and the same difference between the corresponding positive terminals. The impression I got from the answers I got is that yes, this is possible.

Now I wonder what happens in terms of potential difference when you connect two batteries in a series. We know that we'll get the combined voltages across the negative terminal of one battery and the positive of the other. But how does this work? Please tell me if this is a correct way to explain this:


  • Whenever a charged (be it positively or negatively) object touches another object, let's say connected using a conductive material, their charges balance and they become to be with the same electric potential.
  • A battery keeps its nominal voltage between its two terminals. So no matter what is the potential of the negative terminal (with respect to some other reference point) - the positive will always be x volts above it. So if the charge of the negative terminal changes for some reason, the charge of the positive terminal will change correspondingly.

Based on these assumptions, we can say that when we connect the + of one battery to the - of the other, their charges balance, they become to be with the same potential, and since a battery is able to keep the potential difference between the poles, we get together the addition of their voltages.

To compare it with gravitation - let's say one battery is a box of some height (1.5 meters). The second battery is the same box, standing in whatever position relatively to the first. Connecting the batteries is like lifting one box on top of the other, receiving together 3 meters hence gravitational potential of 3*g between the top of the upper box and the bottom of the lower.

Is that correct or am I hallucinating?

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    $\begingroup$ Sounds like you are on the verge of re-discovering Kirchoff's Voltage Law. Yes. Your understanding is essentially correct. $\endgroup$ Commented Jun 9, 2021 at 12:07

1 Answer 1


Yes, the voltages of two batteries in series will add, but both the voltages and the internal resistances can vary depending on the state of discharge.


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