Where are you going to get enough batteries?

If batteries were viable Elon wouldn’t just be talking about them.

Batteries are no where near the cost efficiency of, say, pumped hydro. Nor can batteries touch the overall capacity of pumped hydro. And pumped hydro can’t happen just anywhere - you need the right physical environment for it to be effective.

So yeah, unless you have something more concrete than “batteries, obviously” it is hand waving.