Comment by gumby

> for grid use, where a discharge time of days to months is useful.

Not sure I know the use case for a duration of that length. It's possible today with pumped hydro, but I don't think it's used in that mode.

The DoE's "long duration storage earthshot" effort is loking for 10+ hours, which makes more sense: https://www.energy.gov/eere/long-duration-storage-shot