I ran across this question on another site but I didn't understand the answer that was given. The question asked that if we have a circuit that connected the positive terminal of a 9V battery with the negative terminal of another 9V battery but not connecting the battery together, why would the circuit not work? Electrons doesn't go through the battery and the cations and anions that are needed to balance out the charges are present within each battery. Also, I'm wondering what negative voltage represetns in AC and DC circuits. For example, when I use my electric voltmeter and place the black line (normally placed the negative terminal) on the positive terminal of a battery and using the red line and placing it on the negative terminal, I get a negative voltage reading that is equal in magnitude to the voltage of the battery. I understand that in AC circuits that negative voltage means that the voltage is heading in opposite directions. But the thing is in a DC circuit a negative voltage means that the circuit won't go. Why is this? Are these two negative voltages taking about different things? I just graduated high school so I would appreciate it if you can answer my question in a simple fashion Thanks for any help that you can provide.