Car battery case looks swollen or bulging

Symptoms

• Battery case sides look puffed out or rounded instead of flat
• Battery is warm to the touch even when the car is off
• Weak or inconsistent starting
• Possible sulfur or rotten egg smell near the battery

Likely causes

• CommonOvercharging from a faulty alternator or regulatorExcess voltage can heat and expand the internal battery cells.
• CommonExtreme heat exposureVery hot climates or engine bay heat can accelerate battery case swelling.
• PossibleBattery simply at end of lifeInternal breakdown near end of life can cause gas buildup and swelling.
• Less commonManufacturing defectOccasionally a battery can be defective from the start.

What to do

1. Do not attempt to charge, jump-start, or continue using a visibly swollen battery.
2. Avoid touching the case with bare hands if it appears cracked or is leaking fluid; use gloves.
3. Turn off the vehicle and avoid running it further if possible.
4. Have the battery replaced by a shop or auto parts store rather than doing it yourself if it looks damaged.
5. Ask the shop to test the charging system for overcharging before installing the new battery.
6. Ventilate the area if there's a strong sulfur smell, and avoid open flames or sparks nearby.
7. Dispose of the old battery at a recycling center or return it to the retailer, never in regular trash.
8. Get the charging system verified as fixed to avoid damaging the replacement battery too.

Tools and parts

• Gloves and eye protection

When to call a pro

Always have a swollen battery replaced by a professional or experienced parts store staff member rather than handling it yourself.

Safety