Is a circuit that has two light bulbs and one battery less bright than a circuit that has two batteries and two light bulbs?

There's no general answer to that question. It could go either way, depending on
the specific equipment in use. There are batteries of many different voltages, and
light bulbs of many different resistances. It also makes a difference whether the
two light bulbs are configured in series or in parallel, and whether the two batteries
are in series or in parallel.


For a lamp to operate at its rated power, it must be subject to its rated voltage. So the answer is straightforward: whichever combination results in the lamps each receiving their full, or close to their full, rated voltage will result in them operating at their brightest.