What chemical reactions take place inside a battery? 

In a lead-acid battery, the lead atom does not typically reach a charge of +4. The most common oxidation states of lead in a lead-acid battery are 0 (in metallic lead, Pb) and +2 (in lead sulfate, PbSO₄, and lead dioxide, PbO₂). However, in lead dioxide (PbO₂), which is used as the active material in the positive plate of the battery, the lead atom is in the +4 oxidation state. This is because each oxygen atom has an oxidation state of -2, so to balance the charges in the molecule, the lead atom must have an oxidation state of +4. But it’s important to note that this doesn’t mean the lead atom is short of 4 electrons. Rather, it means that in the context of the molecule, the lead atom has effectively lost 4 electrons to the oxygen atoms. ------------------------------------ An OH-group, also known as a hydroxyl group, cannot have a charge of minus four. In chemistry, a hydroxyl group (OH) typically carries a negative one charge when it is not bound to a molecule and exists as a hydroxide ion (OH⁻). This happens because the oxygen atom in the hydroxyl group attracts the shared electrons more strongly than the hydrogen atom, leading to a charge separation. In the context of a lead-acid battery, the OH-group does not exist freely but is part of the water (H₂O) and sulfuric acid (H₂SO₄) molecules. During the battery’s operation, these molecules participate in various reactions, but the OH-group itself does not carry a charge of minus four.