I know a guy who tried doing something like this and burnt his house down. One of the batteries exploded and took the others with it.
Yes, always have a fire plan in mind when starting a lithium battery project. They go up very quickly and generate a ton of choking smoke. It only takes one oopsie with a screwdriver or dropping a cell to start a fire.
That's why you don't touch Lithium Ion packs unless you know what you are doing. I've repaired many Bosch packs before I tried building my own and seeing the guts of professionally designed and robotically assembled packs after they're a few years old is a very sobering exercise in what to do and what definitely not to do.
There are a bunch of youtubers that go out of their way to give massively dangerous advice to people and I always wonder what their liability situation is.
I was just looking for the comment telling me this is _probably_ a bad idea, so thanks!
I was working on an LED project that involved some reasonably-sized lithium batteries, and the guy in the hardware store said "I don't want to hear about you in the news tomorrow". That really stuck with me, and I say it sometimes when I think someone's going to do something dangerous.