Topic: Reasons for not rebuilding used lithium battery packs
This video is a salutary and chilling description of trying to rebuild lithium battery packs. The presenters demonstrate the pitfalls in trying, and the reasons for not trying.
https://www.youtube.com/watch?v=Mkum7G-0vWg
The message is DON'T try it. You will probably end up with an inextinguishable fire.