My question is a few math operations away from "how much batteries capacity can we deploy to support how much % of renewables in the short-medium term, while still having a stable grid". My "100%" phrasing was sloppy, no need to index too much on it.

Since you're in the industry, maybe you can answer this question and change my mind.

I forget the exact numbers but from my recollection it relies on widespread adoption of EVs and being able to leverage their batteries as part of the grid.

Batteries alone cannot handle all storage use cases, but also including an alternative long term storage mode (syngas, thermal) can get to a 100% renewable grid. Use of hydrogen vs. just batteries cuts the cost of an all renewable grid in Europe in half.