Button batteries are perhaps the most dangerous element of many electronic devices, especially if they are swallowed by children. Here are some details on the potential dangers of button batteries:

1. The chemical reactions of lithium batteries can cause severe burns and other injuries. The chemicals inside lithium button batteries can quickly generate an electric current in a wet environment (such as the human body), causing burns to surrounding tissue. If such batteries are swallowed, they can cause significant damage and may even be fatal.

2. Button batteries are small and can be easily swallowed or choked.  Due to their small size, children may mistake them for food or candy. Once swallowed, they may become lodged in the esophagus or airway, posing a choking risk.

3. Button batteries may leak toxic substances. If a button battery is crushed or damaged, it may leak toxic substances, such as lithium or other heavy metals. This leakage can be harmful to the environment and may cause chemical burns if it comes into contact with the skin or eyes.

Therefore, devices using button batteries should be properly stored and kept out of the reach of children. If the battery needs to be replaced, it should be done by an adult, who should ensure that the old battery is properly disposed of to prevent it from being touched or accidentally ingested by children.