^You are correct, that we, me included, strayed from answering your question. Apologies.
But that’s the nature of responses from helpful people such as myself and others. Especially if we see a flaw in someone’s plan or theory.
It would be like walking past a little old lady struggling to change a flat tire and not offering to help her because she only asked if you knew where a tire shop was, not specifically if you could help her change it.
That, and I’m guessing most aren’t familiar with selling used batteries or trading them in.