Researchers have long known that high electric currents can lead to "thermal runaway" – a chain reaction that can cause a battery to overheat, catch fire, and explode.
Why do car batteries explode?
One of the most common reasons why automotive batteries explode is when the hydrogen gas that is produced during the charging cycle builds up inside the case and is ignited by a spark or a flame. Exploding car batteries send sulfuric acid and fragments of the battery case flying everywhere and these can cause injuries to anyone in the vicinity.
If a path exists into the battery like in a vented battery, the flame may continue into the battery casing, igniting gases that may be inside, thereby increasing the pressure inside the container & causing the container to explode. The explosion reaction is 2H2 + O2 => 2H2O + Heat.
However, the most egregious cause of the Li-ion battery explosions is manufacturer defects. Cheap materials and poor quality assurance can introduce impurities or foreign particles inside the battery, which can create short circuits and increase the likelihood of thermal runaway.
Many modern companies equip their vehicles with sealed gel batteries that are protected from explosions caused by chemical reactions. There is no availability of hydrogen gases in such batteries so there is hardly any risk of explosion.
Lead-acid batteries can explode during overcharge and gassing and when the percentage of hydrogen gas evolved exceeds 4 % by volume. Oxygen and air form an explosive mixture with 4% hydrogen. Hydrogen is an odourless, colourless & a highly inflammable gas. Possible causes for a battery to explode:
Can a frozen battery explode?
These sparks or flames could ignite an explosion if it comes in contact with another flammable component like cigarette smoke. Eventually, if the frozen battery is connected to a charger it can potentially explode due to the level of hydrogen buildup inside the battery casing.