Of these, lithium and manganese dioxide usually cause the most severe burns. When the mercuric oxide batteries leak and fragment, they can cause mercury intoxication as well as burns. Mercury poisoning creates a wide variety of problems, but often begins with vomiting, bloody diarrhea, and severe abdominal pain. It can proceed to decay of the walls of the intestines, vomiting blood, shock, and death. Chronic exposure to high levels of mercury salts causes irritability, kidney disease, colitis, and drooling.
Treatment is aimed at lowering the mercury levels with chelator drugs.
Even when the batteries don't leak, the electrical current passing through the moist tissue of the body can cause significant injury. Controversy shrouds the best way to manage these ingestions. Some recommend urgent surgery or endoscopy to remove all batteries. Others recommend observation alone. I agree with the moderate approach counseled by the National Capital Poison Center.