At the atomic level, why is voltage added when batteries are connected in series?

[shldon]

TL;DR Summary

Need help understanding how exactly from an atomic perspective voltage is added in batteries connected in series.

What exactly occurs at the atomic level when two batteries/galvanic cells are connected in series, resulting in their voltages being added together? I have a rough idea of what happens, but I can't really find a good resource that talks about it in detail.

I know that when you connect the positive terminal of one battery with the negative of another, the electric field will create a current which redistributes the charges so that the terminals connected together will be at the same potential, and the other two unconnected terminals will have a difference of potential equal to the sum of the voltage of both batteries. I think that the reason the connected terminals equalize in potential is due to the absence of a salt bridge (or something similar) at the connection point to prevent the charge buildup.

I can't explain the sum of voltages part though. But I think even though there isn't a salt bridge or equivalent at the connection point, the batteries still have their respective salt bridges and ions still flow momentarily when the batteries are initially connected to equalize the potential at the connection point. But this causes the ends to have a greater potential difference across them. But I'm not sure because wouldn't that shift the equilibrium at both ends?

 

[hutchphd]

I like to think about half-cells. Start on the attached reference...it is pretty succinct.

 

[Borek]

the electric field will create a current which redistributes the charges

This is already hardly at the atomic level, more like your standard macro Physics101.