For old EV batteries where the only reason they need replacement is reduced capacity I wonder if they might be useful in some stationary applications? I'd love to have a whole-house battery backup system for the occasional power outage, but systems with new batteries are too expensive.

An 80 kWh battery, say, that has lost half its capacity would have been enough to get me through most outages I've seen since moving into my current house 15 years ago without me having to even try to reduce power during the outage. The one or two outages where that would not have been enough, it would have been sufficient to just dress warmer, turn the thermostat down a little, and avoid doing laundry.

I'd be interested in this as long as the price per kWh of the degraded battery is significantly lower than the price for a new battery with the same capacity. The degraded battery is going to be good for much less cycles than a new battery of the same capacity, so it should cost less.