Simple voltmeter from Harbor Freight would set you back a few bucks and would give you instant voltage... Or you could snag a digital one from Fleabay pretty cheap and that solves that problem.
Just seems like the discussion is talking about a heck of a lot of work (and investment) for some lights that could be set up in 15 mins or so with about $40 worth of battery and wiring! I've kicked this same idea around for our kart, and I think battery power is the route I'll go, especially since I'm pretty well equipped for it with all the power wheels gear we have.