"An important alternative to consider when assessing coin-like objects is button batteries. These are very similar in appearance to coins, but typically have a slight step in profile with an inner ring when viewed en face."
"Button battery ingestion is potentially fatal. Sodium hydroxide accumulates at the negative electrode as a consequence of tissue fluid hydrolysis. The resulting progressive ulceration can cause tracheo-oesophageal fistula or death 5-7. The oesophagus is particularly susceptible to damage due to weak peristalsis and to the narrow calibre which ensure continued close apposition of tissue to the battery. Oesophageal button batteries should be removed endoscopically as an emergency 9. Early and frequent ingestion of honey prior to endoscopic removal has been found to provide a coating which decreases the incidence of mucosal injury and full thickness tissue necrosis 8."
"Standard radiographic investigation of foreign bodies in children should include plain radiographs of the neck, thorax and entire abdomen 4. In one study ~65% of ingested foreign bodies were radiodense 2."