If I connected 2 batteries together in series Positive-Negative-Positive-Negative, I've read many times the voltage (joules/coulomb) adds. I cannot understand what is going on to cause this at the ATOMIC level. Electrons in a battery are produced by a redox reaction and are attracted to the positive (cathode) part of the battery. The only way to do this is if one connected a wire from Positive and Negative side of the battery. However, if 2 batteries were connected in a P1-N1-P2-N2 with a wire from P1 to N2, when the electrons from N2 make it to P1, aren't they attracted into the cathode electrode of the battery? What keeps the electrons from moving on past P1? Electrons get the voltage, or potential energy, from the chemical reaction, so how does it get the voltage of 2 chemical reactions, i.e. why voltage adds in this case. Can you explain at the small scale of what forces are making the electrons gain energy and move the way they do? Thanks for any help to help me understand.