Can someone explain to me why they might have gone with this strange pricing model instead of the very simple revenue sharing model that Epic uses?

The main problem with lithium ion battery fires is that the reaction is self-oxidizing, so you can’t put it out by just smothering it. You actually need to cool them down enough so that they don’t re-ignite. Plus, once they’re damaged, even if you do cool them down enough they’re much more likely to short and re-ignite themselves again anyway.

Consider the “fire triangle” - fire needs three things: fuel, oxygen, and heat. With, for example, gasoline fires you can take away either oxygen OR heat to extinguish them, but with lithium-ion battery fires you have to take away the heat to extinguish them.