Swallowing Button Batteries Causing More Severe Injuries, Deaths In American Children (Medical News Today, May 2010). Here’s a quote:
“When button batteries…get stuck in the throat they can cause severe tissue damage within just 2 hours of ingestion. Further damage can also ensue, such as paralysis of the vocal cords, narrowing or stricture of the esophagus or food pipe, a hole connecting the windpipe to the food pipe (tracheoesophageal fistula), or severe internal bleeding as a result of a hole into a major blood vessel.
“In most cases, the button battery passes through the body and comes out in the stool, but sometimes it gets stuck, and these are the cases that cause problems. For instance, a battery stuck in the esophagus or food pipe causes tissue damage because of the alkaline hydroxide that results from the electrical current set up around the battery. This burns the tissue.”
They also note that the worst outcomes were from large-diameter (> 20 mm) lithium cells.
I’ve heard of intestinal perforations in kids eating batteries. It sounds like a depleted battery might not be as dangerous if it gets stuck in the digestive system, though a “dead battery” of any type might have enough “juice” left to injure mucosa.