According to this video [0], each motor has its own battery. So presumably they're in the cylindrical enclosures under each motor (it briefly shows one being replaced).
I just saw the video, I think that's plausible and notably the test flight seems last only few minutes without the magic "hybrid technology" they mention in the presentation, as expected. I agree with one think the guy says in the video, the only purpose of that machine is to make people enjoy the thrill of flight, aka amusement parks.