If you add a battery to a series circuit what will happen to the current in the circuit

If there wasn't any battery before, then there was no current

in the circuit before, and there IS one now. That's just about

the greatest change possible.

If there WAS a battery there before and you added another one

in series with it, then there are a few different possibilities for the

effect on the current in the circuit:

- - If the new battery has the same voltage as the original one,

AND you connect the new one so that they're both in the same

direction, then the current in the circuit will become double the

original current (twice as much as it was before).

- - If the new battery has the same voltage as the original one, AND

you connect the new one so that they're in opposite directions, then

the two batteries cancel each other, the total voltage becomes zero,

and the current in the circuit completely disappears.

- - If the voltage of the two batteries is different AND you connect

the new one so that they're both in the same direction, then the

current in the circuit increases, by a factor of

(sum of the two battery voltages)

divided by

(voltage of the original battery alone).

- - If the voltage of the two batteries is different AND you

connect the new one so that they're in opposite directions,

then the current in the circuit decreases, by a factor of

(difference of the two battery voltages)

divided by

(voltage of the original battery alone)

and the current flows in the direction of whichever battery has

the greater voltage. If the new battery has greater voltage than

the original one alone, then the current reverses, and flows in

the opposite direction.

I think that covers all the possibilities.