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A button cell (also known as a watch battery or a coin battery) is a small, single-cell battery that is shaped like a squat cylinder, resembling a button. They are typically 5 to 25 mm in diameter and are made out of stainless steel.

Button cells are found in many everyday things. Some examples are:

• Watches
• Calculators
• Hearing aids
• Car key fobs
• Small toys
• Medical devices
• Computer backup power
• Certain types of phones
• Life support

Most button cells are made for one-time use. This means they are meant to be thrown away when they run out of power. Some button cell batteries can also be recharged, meaning they can be used multiple times without needing to be thrown out, although they have lower capacity than disposable ones.

Inside, different chemicals are used. Some common types are:

• Alkaline: Higher capacity than zinc-carbon.
• Lithium: Most common variant. Lasts a long time and is often used in computer memory.
• Silver oxide: Higher capacity for devices with cut-off voltage.

Button cells are dangerous if swallowed. When a button cell gets stuck, it can cause very internal burns inside the body. If this happens, it is a medical emergency. Failure to remove the battery can cause permanent internal damage to the body, including very extreme constipation, or even death in extreme cases.^[1]

To help combat this, companies now put a bitter coating on the batteries to reduce ingestion by children from swallowing them which tastes terrible as confirmed by "The Verge".^[2]There have also been some very severe cases of very young children being exposed to the zinc contained inside these button cells, which confirms the danger with eating them.^[3]