Because lithium cells degenerate in a fairly linear fashion…
by the time they have gotten down to 75%, that is a noticeable reduction in range for a BEV- but they still have years of life left in them- just reduced capacity…
Now you can’t simply ‘add a second set’ to an EV- the extra weight means a further reduction in range- but for a house that doesn’t need to haul its batteries around- well, it makes sense to reuse those cells in a ‘powerbank’- especially as most houses demands are far less than even the best EVs…
Many houses use 10kwh a night or less, so a 100kw ex car battery pack, even at 75% of its original capacity, will run a house for over a week (picking totally random numbers here, but in the ballpark for modern BEVs)
So the household use is both far less demanding (meaning the ‘wornout’ ex BEV battery pack will last even longer in its new role as a ‘powerwall’) plus allows the reuse of those aging batterypacks without needing a ‘complete recycling’
So rather than them ‘going to waste’, you can reuse them for probably another 10–15 years minimum- keep the cycle rate down and they may last even longer…
Sure ‘new batteries’ in the powerbank might last longer- but they will increase the price significantly, and mean you still have a large number of cells that have a fair bit of life lying around with no use…
Hell, even if they had only 25% of their original capacity- you can’t put 4 in a car and expect anywhere near the range- but put 4 in a house and- who cares????
Its literally a single wall in a garage installation, even with four ex BEV packs…
This is a 100kwh Tesla battery pack (its the ‘floor’ in a Tesla)- obvious by the ‘dimples’
You could stack two vertically on the smallest wall of of a single car garage and another four down the ‘long wall’ of one- do the same on the other ‘long wall- and you have 10 x 100kwh of ‘original’ storage- even if they were as bad as 50% capacity only left- thats still half megawatthour of storage- for a house using 10kwh a night- thats 500 hours of use- non stop- without a single electron of electricity coming into it…