CAISO's own documents quote battery capacity in MW. So I don't think you can just blame journalists.

"Battery storage capacity grew from about 500 MW in 2020 to 13,000 MW in December 2024"

https://www.caiso.com/documents/2024-special-report-on-batte...

As another commenter notes, utilities are interested in "capacity on call" i.e. instant power generation.