What phenomenon is commonly caused by overcharging mobile device batteries?

Overcharging mobile device batteries can lead to the phenomenon of swollen batteries. When a battery is overcharged, the chemical reactions within the battery can produce excess gas, causing the battery casing to expand. This swelling can not only be a sign of damage to the battery but can also pose safety risks, such as leaks or even rupture, which could potentially lead to fires.

While overcharging can affect performance, lead to charging issues or contribute to poor battery health in various ways, the most identifiable physical manifestation directly associated with the act of overcharging is battery swelling. This makes it the correct answer in the context of the question. Understanding this can help users better monitor the health of their devices and take necessary precautions to prevent damaging their batteries.