Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: series battery discharge

Learn more physics!

Most recent answer: 10/22/2007
Q:
when you connect bateries in series, the positive terminal of the batterie connect to the negative bottom of the next batery. so i assume that electrons flow directly into the positive terminal. i would have thought that tha batterie will discharge itself before it can do any work. i know iím wrong but i cannot figure it out. would you please explan it to me.

dave
- dave (age 19)
vancouver, bc, canada
A:
Before  you hook two batteries together, the two positive terminals have the same voltage and the two negative terminals have a different voltage, also the same as each other. (I'm asuming that overall the batteries are initially equally near ground.) When you hook the postive terminal of one to the negative terminal of the other, you're right that some current will flow, since the starting voltages are different. A very tiny amount of charge transfer will raise the overall voltage of one battery and lower the voltage of the other (because they now have a little net charge) so that the terminals you connected will be at the same voltage. The total charge transfer was tiny (electrostatic forces are big) so that in the process the batteries discharged a negligible amount. The voltage drop between the positive and negative terminals on each is unaffected.
Until you complete the circuit, there's no way for much current to flow, so the batteries will remain charged. That's another way of saying that charge buildup anywhere quickly creates a voltage that prevents further current flow. In a complete circuit, charge can keep flowing without building up anywhere.

Mike W

(published on 10/22/2007)

Follow-up on this answer.