Batteries are not power sources, but storage. The energy still has to come from somewhere, and power generation won't magically become 10x cheaper overnight. No matter how cheap battery storage becomes.
But it IS crucial for removing bottlenecks & replace fossil fuels.
Imagine for a moment that batteries with decent shelf lives are free.
You build a power plant on a geothermal vent in Iceland. The electricity it produces is plentiful and cheap. You run it full tilt charging batteries.
You ship those batteries to wherever you need cheap power, and send them back empty. This works with hydro, wind, solar, ...
Batteries do drive down energy costs because even ignoring transmission lines, they let you move energy in both space and time, pushing all energy costs towards the cost of the cheapest means of generation on its best day.