What dangerous gas is produced when charging a lead-acid battery?

When charging a lead-acid battery, hydrogen gas is produced as a byproduct of the electrochemical reactions that occur. During the charging process, the application of electricity causes the water in the electrolyte solution to break down, resulting in the formation of hydrogen and oxygen gases.

Hydrogen is flammable and can create an explosive mixture if allowed to accumulate in confined spaces, making it critical to ensure proper ventilation when charging these batteries. Understanding the risks associated with hydrogen production is vital for safety protocols in environments where lead-acid batteries are used.

The other gases listed have different sources and implications. Oxygen is actually produced alongside hydrogen in smaller amounts during the charging of the battery but is not considered dangerous in the same way hydrogen is. Hydrogen sulfide is a toxic gas often associated with organic matter decomposition and certain industrial processes, and cyanide is a highly toxic compound used primarily in specific chemical manufacturing contexts, not related to battery charging.