I will admit you are right when someone installs a grid scale battery with 7 days of storage at at least 100MW of output

Batteries are only one of many inputs needed for grid storage.

Batteries utterly dominate the cost of grid storage... everything else is a rounding error.

You're welcome to go find your own data of course, you'll struggle to find more direct numbers because significant grid storage has only become affordable in the last few years.