What kind of problems do swallowed batteries cause?

Many of us "know" that coin cells need to be kept out of reach of young children as swallowing them is bad.

I wanted to find out "what kind of bad" swallowing a coin cell was, so that information may help select a better alternative. The best information I found was from the US National Capital Poison Centre, which says this about itself:

The National Capital Poison Center, founded in 1980, is an independent, private, not-for-profit 501(c)(3) organization. In recognition of its high quality, the Center is accredited by the American Association of Poison Control Centers. The Center is not a government agency.

They have a page all about Mechanism of Battery-Induced Injury which is a good meta/literature search. Their key findings are that there are three main mechanisms of injury, in priority/severity order:

1. Generation of an external electrolytic current that hydrolyzes tissue fluids and produces hydroxide at the battery’s negative pole,
2. Leakage of battery contents, especially of an alkaline electrolyte, 
3. and Physical pressure on adjacent tissue.

Personally, I was expecting mechanism 2, but not mechanism 1. I wondered if we could recreate the mechanisms in a semi-controlled way, as a means to evaluate any safer alternatives. Read on to the next log if you want to see more.

Possible ways to avoid these injury mechanisms.

So, now we have insight into what mechanisms of injury battery swallowing causes, we can start to hypothesise what measures could avoid or reduce the severity of a swallowed battery. By the way, as we're going to look beyond conventional batteries, we should probably use a term like "swallowed energy store" instead of "swallowed battery".

• Make the energy store too big to swallow (or permanently fix it to something so large the whole assembly can't be swallowed).
• Provide ingress protection such that tissue fluids (such as mucus in the throat) don't contact conductors that can source/sink significant current.
• Reduce the total amount of energy stored such that it produces less hydrolysis of tissue fluids.

We'll consider and test some or all of these in future logs.