It is known to all that almost all batteries are lithium batteries now. When charging, the lithium electronic polymer will produce a small amount of gas when it is discharged, which will cause a slight expansion, that’s normal. Overtime that gas will build up and cause the battery to expand.
Other Causes of Laptop Battery Swelling
1- overcharging.
2- Manufacturing defect, such as no protective plate inside, unreasonable distribution of positive and negative plates, uneven distribution of lye (electrolyte),etc.
3- Exposure to high temperature, the battery will be overheated and deformed.
4- Deep discharge.
5- Damage to the battery, such as damage to the membranes that separate the internal layers of the battery.
6- Natural aging.
7-Using a charger of the wrong voltage rating.