I poorly communicated the idea in that part of my comment to be honest, my apologies. It's currently a battery in the sense that it exports during the wet season and imports from VIC during the dry season. As mentioned, it'd be a "proper battery" where it can "charge" from renewables (or, dreadfully, fossil) with the link you and I provided in this subthread.

Hydro resources are an important component of future grids, as long duration battery storage is pricey (although short duration storage such as Tesla's install at the Hornsdale Power Reserve is critical for ancillary services like frequency response and synthetic inertia, to keep frequency and voltage within tolerances when a thermal generator trips or renewables drop offline).