I understand your concern, I totally agree that the volatility isn’t ideal, but putting it in a steel box outside your house isn’t that beyond the scope for a diy-er. Envision it the same way a generac sits outside and ties in to your house but with a safe enough enclosure.

As long as you check the cells you use when you deconstruct the car battery it should be fine. All the projects I watch online they don’t even need the liquid cooling system that it utilized when it was in the car because the discharge rate is so far below the C rating the battery that they don’t generate great like when they are in cars

I understand that cell could go bad though at any time, so the box is necessary imo