Galacticraft adds a normal battery, a low energy output nuclear battery, and a creative only Infinite battery. It would be nice to see this mod support Galacticraft's batteries.

All electric Floodlights support batteries from Galacticraft. I just check this using Galacticraft Core 1.12.2-4.0.2.229.

If you're using an older version of Galacticraft, try to update it and then let me know if the problem still exists.