Which gas is known to come from batteries charging or water in extremely hot fires?

The gas that is known to come from batteries charging or from water in extremely hot fires is hydrogen. When batteries, especially lithium-ion batteries, charge, they can produce hydrogen gas as a byproduct, particularly if they are overcharged or experience a failure.

In extremely hot fires, water can undergo a process called thermal decomposition, where high temperatures can break down water (H2O) into hydrogen (H2) and oxygen (O2). This form of hydrogen can contribute to the risk of fire and explosions due to its flammable nature.

Considering this information, hydrogen is recognized for its potential to be released under these conditions, making it the correct answer for this question about the gases produced during specific scenarios involving batteries and extreme heat.