What is one of the chemicals in a battery?

This varies depending on the specific battery "chemistry" used.

• the old carbon-zinc batteries used - carbon, zinc-Mercury alloy (with iron grains contamination in the zinc), zinc chloride paste, water, manganese dioxide (to suppress hydrogen gas formation), porous paper separator
• modern alkaline batteries use - carbon, zinc, potassium hydroxide paste, water, manganese dioxide (to suppress hydrogen gas formation), porous paper separator
• lead-acid batteries use - lead, sulphuric acid, water
• nickel cadmium batteries - nickel oxide hydroxide, cadmium, potassium hydroxide paste, water, porous paper separator
• lithium manganese batteries - lithium, manganese dioxide, lithium perchlorate paste, propylene carbonate, propylene dimethoxyethane, porous paper separator
• lithium ion batteries - lithium nickel manganese cobalt oxide, carbon, lithium perchlorate paste, ethylene carbonate, porous paper separator
• etc,