You also need to account for combustion energy, for example, from Barsukov & Qian, p. 94
However, one of the side effects of organic electrolytes is that when the temperature exceeds a certain limit depending on battery chemistry, the reaction between the active material and electrolyte releases heat and becomes self-supporting (thermal runaway), which can cause a fire, explosion, or venting of electrolyte. Just how destructive can such an event be? It depends on the amount of energy released. Let's compare the energy of an 18650 Li-ion battery with that of a well-known destructive device, say, a hand grenade filled with TNT. TNT releases energy of 4.1 kJ/g. A Li-ion battery stores 0.250 Wh/g, which corresponds to 0.93 kJ. This is about one-quarter of the TNT energy. But — and this is a big difference with traditional batteries that have a water-based electrolyte — a Li-ion battery has additional energy in its organic electrolyte! In case of combustion, it will also burn. So will polymer separators. As reported in a safety analysis , the energy released by the burning of up to 10 g of electrolyte and 1.6-g separators contained in an 18650 cell is 280 kJ. Given the cell weight of 40 g, we get 280/40 = 7 kJ/g of combustion energy. So, taken together, the electric and material burning energy per gram of Li-ion battery is around 8 kJ/g, close to twice that of TNT! Comparing an 18650 cell with a typical hand grenade (U.S. M67, with 180 g of explosive), it takes only five 18650 cells to exceed the hand grenade's energy! A typical notebook battery pack (3 serial/2 parallel, 3s2p) has six cells, so it has more combustion energy than a hand grenade. I trust this will make you pause a moment.
Fortunately, battery combustion is not nearly as fast as that of explosives ...