If your vehicle is showing battery case looks swollen, cracked, or bulging, here are the most likely causes and the parts you'll need to fix each one.
A failing voltage regulator can send too much voltage to the battery, causing the internal electrolyte to boil, produce excess gas, and swell the case.
As a battery ages, internal plates can degrade and touch, creating a short circuit. This generates massive internal heat and gas pressure, causing the case to bulge.
A discharged battery can freeze and crack in extreme cold. Conversely, severe underhood heat without proper shielding can cause the plastic case to warp and bulge.
If the battery securing bracket is tightened too much during installation, it can stress and eventually crack the plastic battery case.