Question

In a series circuit, as more batteries are added what effect does it have on the bulbs in a circuit . Will the bulbs get brighter or stay the same?

Answer 1

If the batteries are in series too, then the more batteries,
the more voltage across the light bulbs, and the brighter
they will all burn. 

(Until you add the battery that causes the weakest bulb
to burn out.  Then they ALL go out.)