An e-cig, mod or the internal vape battery explodes when it overheats and a runaway chemical reaction occurs. A modern lithium battery is designed to be operated within certain power and temperature ranges. The battery is not designed to be overheated or over-discharged beyond its designed limits. If your mod has lower resistance, it can draw energy from the battery beyond the safe limit. When this occurs, the chemical structure designed to store energy instead begins a new reaction causing energy to release uncontrollably. The battery ultimately catches fire – continuing to burn until the entire batter is consumed.
For a fortunate few, the heat may disperse before the battery catches fire. However, there is a substantial risk that the heat and gas will not in fact disperse – particularly if the vape battery is enclosed in a mod device – ultimately resulting in a dangerous build-up of energy and a quick release: a vape battery explosion.