Button cell batteries contain either mercuric oxide (with up to 25 mg of mercury) or silver oxide. Lithium batteries contain lithium. Lithium IS explosive and/or flammable in reaction with air or water.
Nickel-cadmium batteries - up to 50% of the weight consists of cadmium. Cadmium is a heavy metal and possible human carcinogen. Because of the extreme toxicity of these batteries it is ESSENTIAL to recycle them.
Lithium-ion batteries may contain manganese, cobalt, nickel, chromium, or aluminum. These are heavy metals and can be highly toxic.
Lead-acid batteries (wet-cell) are flammable and explosive. Leaking battery acid is highly corrosive, and battery acid fumes are highly irritating and dangerous to the eyes. Small sealed lead-acid batteries are used as a power source for emergency lighting, wheelchairs, and other medical equipment.
ALL RECHARGEABLE BATTERIES CONTAIN HAZARDOUS MATERIAL.