Battery acid is a highly corrosive liquid that is used in lead-acid batteries. It is composed of sulfuric acid (H2SO4) and water. The pH of battery acid is 0, which means that it is extremely acidic.

Stomach acid is a digestive fluid that is produced by the stomach. It is composed of hydrochloric acid (HCl) and water. The pH of stomach acid is 1-2, which means that it is also extremely acidic.