The energy released during a fire is higher than what is accessible by discharging the battery. Here's one paper describing ratios from 1.25 to 5 depending on access to oxygen during the combustion.
The relationship between energy stored and energy released was mostly determined by how big the batteries were, not their state of charge. Only 4 of their tests varied state of charge, and those were all in vacuum (with cells #1 & #6), and state of charge was never below 60%.