How number of batteries affects bulb brightness?

Well batteries are full of energy the more batteries more light from the bulb. But sometimes the way the batteries are in can cause change in a effect and reaction

There's not enough information in the question to answer it.

- - If the batteries are in series, then

more batteries = = > brighter bulbs.

- - If the batteries are in parallel, then the number of batteries

has no effect on the brightness of the bulbs.

These two predictions apply equally well whether the bulbs

are in series or in parallel.