"Wall wart" is slang for those ubiquitous black plastic cubes the have the prongs to plug into the wall out let and provide low voltage AC or DC for small applicances, chargers and etc. Most folks have a bunch of them lying around from dead electronics. As you're using incandescent bulbs you wouldn't need to worry about AC/DC but assuming your batteries are wired in series about 3 volts. Check you junk drawers, the wall warts are usually marked.
You would need to cut of the plug and splice the wires to the wires on your lights, with bulbs no need to worry about polarity.
