Immediately remove the swollen battery from the equipment it is in. A battery expands due to overcharging. High rates of overcharging will cause a battery to heat up. It accepts more current as it heats up, heating it up even more. This cycle of overheating is called thermal runway and it is able to destroy a battery fairly quickly, sometimes in only a few hours. Heat that causes the battery to swell.

The battery is not usable. Recycle it a local battery recycling facility. This battery needs to be replaced immediately.