

Slim chance is the objective way of expressing a low likelihood. Fat chance is a colloquial expression using irony. You say one thing but mean the opposite. It’s more often used as just a quippy two-word reply.
Language doesn’t make sense. When flammable and inflammable can mean the same thing, all bets are off. You cannot make sense of these things; you can only accept them.





I just had a quick search about temperatures in a crematorium. Around 800 °C. A structure that can withstand that sort of temperatures is probably also able to withstand exploding batteries. If I remember the Galaxy 8 disaster, they go pop and then it’s just mostly a chemical reaction releasing heat and gas. 30 batteries might be a lot. It may not end up destroying the place but it will possibly leave it in need of repair.
Why do you want to create this sort of fireworks show in a confined space where under normal circumstances nobody will be present to witness it?