Ok just to note some reasonable baseline numbers :
This Alibaba seller wants $468 including shipping for 4 * 280 Ah * 3.2 volts. This works out to 3.584 kWh. And you can then slap on a 100 amp DALY BMS for
$56 from Amazon.
So (468+50)/3.584 = $144 a kWh. Presumably you need a few more bits of wire and heat shrink to hit the $150 mark, or maybe David Poz uses a less crummy BMS like the overkill solar one, and a 48 volt pack. This would be (1,748.72 + 120) / 14.336 = $130 a kWh.
Please note that these are not even Eve cells though they may come from the same factory. You are supposed to compress the cells which sounds easy but appears to be a massive pain, there are several threads on this and various contraptions people have come up with. You don't get a metal box to help contain the fire in case something happens. Nor a circuit breaker, fuse, monitoring board, nor does it neatly slide into a server rack. And you will need 4 of these to hit the 48V the growatt all in ones usually require.
Still you appear to get 14.336 kwh for the price of a little more than just 1 48volt/5kwh premade battery.
Honestly, at these prices. You could order 2 extra batteries for spares. Swap out the ones that go bad. It might work for a decade.