Grid battery deployment is faster than EV market penetration in the USA. This is not something that can siphon off a fraction of EV batteries. It is a huge market in its own right.

What would be considered ruined Leaf EV batteries that have significant range loss (20% to 50% degradation, for a car that went around 60 miles with a full battery) are being used to cover peak load right now in California and have been used to do so for years.

https://www.youtube.com/watch?v=JqlOlqK_ot8

2nd life use cases for cheap, mass produced batteries like this are more common than you think.

But that isn't a mainstream case. It's notable for being weird. The 1000x larger Moss Landing battery facility just uses new, off-the shelf BESS units from LG.

No grid operator going to mess with scrap batteries. Even for home player new cells are so cheap that it's not worth messing around with used ones (esp when considering liability and insurance). Might work in third world countries tho who have even more appetite for reliable power.