Batteries will always be the expensive choice of storage. There will be a certain amount of it anyway. But utilities, for bulk storage, will favor cheaper alternatives.
Perhaps it will be the expensive choice, but I expect batteries produced for cars to be moved to grid storage when any given vehicle's capacity drops below the level useful for transport, and the combined capacity of the reused batteries of a fully-electric-car-nation, even with those batteries in a worn state, will suffice for grid storage.
My guess is this transition will take 15-20 years to complete, but I have low certainty on that.
I'm kinda leaning towards expecting batteries (specifically batteries and not storage in general) to be the first way a continental power grid gets to 100% renewable, even though I prefer the aesthetic of a global grid. But I don't have any skin in the game, and wouldn't bet against e.g. a cheap high temperature superconductor grid or liquid hydrogen.