Catenaries can stretch up pretty high. This is a bit of gadgetbahn trickery, using batteries shifts cost from up-front capital improvement projects to operating and maintenance cost (managing vehicle charge levels and replacing batteries) and it eliminates one avenue for opponents of new transit to criticize (unsightly wires ruining the anesthetic of our beautiful car-choked city). It is a technically worse solution, but it's a relatively mild departure from trains/trams as far as gadgetbahns go, and if they can leverage the novelty and the political benefits to build more transit to serve more people than they otherwise would have, good for them. Time will tell if this approach pays off, the world is littered with failed gadgetbahns, but also sprinkled with a few success stories