Lithium-ion batteries contain an amount of lithium metal and in case of a fire they can be doused with water. Lithium-metal batteries on the other hand require a Class D fire extinguisher. Thermal runaway events involving lithium-ion batteries can occur rapidly and can often be quite violent, involving toxic smoke and vapours, flames, and metal projectiles. Warning signs to look out for in a device or battery include: Pungent odours. Discolouration, blistering, bulging, or swelling of the casing.