California isn't exactly known for water management practices, though sure there are storage systems that use kinetic potential as a battery. In theory that can be used at very large scales, if the water and elevation is available for use.

Is be really curious how the math works out with regards to how much water would be required for say 3 days of use in LA. That may even be an over estimate of storage needs given how few rainy days they get.

And for lithium batteries, maintaining an overcapacity drastically increases the lifetime by reducing the depth of the cycle. e.g., you get vastly more cycles at %50 DoD vs %80. This would increase the lifespan to be many decades

California is already planning a giant off-river reservoir that will be dependent on pumping to fill. If it could be set up to kick in instead of curtailment it could be a win win.

The California Environmental Quality Act (CEQA) makes it extremely difficult to build new pumped storage facilities. It's possible in principle but will take many years to get through the construction permits and inevitable lawsuits.