Those tiny, common "button" batteries can pose a big threat to children if swallowed, toxicologists warn.
The round batteries are used in items such as toys, musical greeting cards, remote controls, calculators, watches, key fobs, flameless candles, hearing aids, games and flashing jewellery.
"If a button battery ingestion is even suspected, quick medical evaluation should be a priority," Dr Donna Seger said in a news release from the Tennessee Poison Centre. She directs the centre, located at Vanderbilt University Medical Centre in Nashville.
In 2014, about 3,500 reports of people, mostly children, swallowing button batteries were made to poison centres in the United States. Each year, more than 2,800 American children require emergency care after swallowing button batteries.
In most cases, the batteries pass through the digestive system without causing harm, the toxicologists explained. But if a button battery lodges in the oesophagus, it can produce an electrical current that burns through tissue and major blood vessels in the neck. Some children in this situation have died.
Symptoms of a button battery lodged in the oesophagus can include chest pain or tightness, coughing, foreign body sensation or bloody vomiting.
An X-ray is recommended as soon as someone swallows a button battery, according to the poison centre.
Prevention is the best approach. Keep items with button batteries out of the reach of children, the toxicologists said.