Why Do Batteries Swell Up?
So why do batteries swell? Lithium-ion batteries create a chemical reaction that generates power for modern electronics. However, as a battery ages the chemical reaction that occurs inside the battery no longer completes as intended, which results in the creation of gas. In more technical terms, electrons oxidizing inside the battery create a toxic gas that forces the battery to expand. Believe it or not, this process is actually a safety mechanism designed to trap the toxic and corrosive gases.
In addition to swelling, if the battery's multiple layers of chemicals refuse to maintain their proper integrity within the battery, due to damage or gas creation, fire, and even explosion can occur. The rare explosive reaction has been known to happen to Galaxy Note 7's and hover boards, which resulted in strict regulations being placed on mailing batteries, carrying them on airplanes, and the complete recall of certain devices.