Toyota is recycling old EV batteries to help power Mazda's production line

Those who TL;DRd - it's for the factory, not the cars!

Old EV batteries are great for energy storage. A worse weight-to-capacity ratio doesn't matter for batteries sitting on the ground. A battery that holds only 70% of its original capacity is considered worn-out for EVs (and even replaced under warranty), but grid storage isn't driving anywhere, so any capacity left is still useful.

If you take car EV batteries and use them for stationary storage when past end-of-life, the fire risk becomes fairly substantial because EV batteries often have a little water ingress, physical damage etc.

It can be solved by isolating each battery in its own steel box, but that gets fairly expensive fairly fast.

I've seen a video on the youtube where a battery recycling company does this; they leave the car battery packs in their original housing, which I presume is water resistant enough. Each unit is also connected to a controller, which I also presume monitors battery health, temperature (assuming temp sensors on car battery packs), voltage, etc. If a unit is dying they can safely dispose of it, else, the units were out in the open and with several meters in between, meaning any fire would be unlikely to spread to something else and there's plenty of access opportunities.

Very space inefficient though, but there's more than enough of that in the US.