Battery acid is dangerous because it's just sulfuric acid diluted with water. The concentration of the sulfuric acid in batteries varies between brands, but on average, the concentration level is 37 percent.
Sulfuric acid is corrosive by nature and can melt body tissue on contact. When sulfuric acid comes into contact with soil, it contaminates the soil for an extended period. The actual length of contamination varies depending on the concentration of the acid. Due to how dangerous sulfuric acid is, batteries containing sulfuric acid have to be recycled at a special facility. It's considered illegal to dispose of these types of batteries in the garbage.
Sulfuric acid, which is sometimes called the oil of vitriol, is not only corrosive, but poisonous as well. As a result, it can be fatal if swallowed. Studies also suggest acid mists containing sulfuric acid can cause cancer. The risk of cancer is dependent on the level and duration of the exposure.
If sulfuric acid is inhaled, it can cause damaging affects to the upper respiratory tract and mucous membranes. It can also cause lung edema, which is a medical emergency. Symptoms suggesting sulfuric acid has been inhaled include irritation of the throat and nose, as well as labored breathing.