Well, you can start with https://en.wikipedia.org/wiki/Lithium-ion_battery#Safety https://en.wikipedia.org/wiki/Lithium-ion_battery#Safety How big an "event" o

Well, you can start with https://en.wikipedia.org/wiki/Lithium-ion_battery#Safety https://en.wikipedia.org/wiki/Lithium-ion_battery#Safety How big an "event" occurs when a battery is damaged to the point of self-immolation is correlated with its level of charge. A fully-depleted battery won't do much if damaged. A fully charged battery will vary from "it gets really hot" to "boom," depending on how it is constructed. Thus, if you have a LiIon battery that you want to dispose of, it's always better to safely discharge it as low as it will go before storing or transporting it. Lithium-polymer ("pouch") cells are cheap to make and are incredibly energy-dense compared cylindrical cells (such as the classic 18650), but are far more likely to go kaboom. Unfortunately, they make up the majority of our Lithium-powered gadgets. LiFePo4 cells are MUCH more stable than either traditional lithium style, handle over-charging better, and survive far more charge/discharge cycles. The tradeoffs are that they are a bit more expensive and are slightly less energy-dense. I have also never seen them in "pouch" form, so I don't know if they can ever replace lithium-polymer for cell phones/tablets. But they are pretty popular now in power tools and car/bike batteries.