I have always been a tinkerer. I have added electric motors and gas engines to bicycles, tricycles and quadracycles that I have purchased or built, along with fairings etc... I bought my first 3D Printer with the intention of making parts for these kinds of projects.
I have also taken apart battery assemblies from tools, toys and electronics to repair and refurbish them. Lithium battery packs are temperamental little beasts. When you have cells that are bulging that is a warning sign that you should probably not be messing with them. That has never really stopped me even though I am aware that they can catch on fire or explode.
The problem is that even with redundant safety precautions the lithium based battery packs in electric vehicles have so many cells that out of thousands of battery packs a certain percentage are going to have problems that are not user serviceable and some are likely to catch on fire. When they do there can be big problems especially if the car is inside someone's home while they are charging it.
My friend worked as an engineer assessing the safety of lithium based battery packs. Since that time he will not allow any lithium based devices to be charged in his house while his family is sleeping... even cell phones and laptops which have circuitry and cells which have low charge and discharge rates. The fumes that come from burning battery packs are very toxic.