What Causes a Battery to Swell?

[LeEmmett]

Battery swelling can be caused by issues with battery manufacturing quality, intense reactions due to short circuits, or prolonged inactivity of the battery. Below are detailed explanations: Issues with battery manufacturing quality: Uneven electrode coating and relatively crude production processes. Intense reactions due to short circuits: Generates a large amount of heat, leading to the decomposition and vaporization of the electrolyte, which causes the battery to swell. Prolonged inactivity of the battery can also cause swelling: Since air is conductive to some extent, leaving the battery unused for too long is equivalent to a direct connection between the positive and negative terminals, resulting in a slow short circuit.

[McVictoria]

Last month my car wouldn't start, and when I popped the hood I found the battery swollen like a balloon. The mechanic said overcharging is a common cause, just like when a faulty phone charger makes the battery bulge. During summer when cabin temperatures soar above 50°C, the electrolyte inside the battery vaporizes into steam trapped within. If charging voltage exceeds 15V it's especially dangerous - you should check if the alternator voltage regulator is faulty. Once I kept using a 5-year-old battery without replacement - the aged/sulfated plates couldn't dissipate heat during charging, causing swelling. The scariest scenario is blocked vent holes preventing gas release, which can deform the casing. Remember never attempt DIY removal of swollen batteries - the sulfuric acid inside can cause serious burns if leaked.

[VanJocelyn]

I've been in auto repair for ten years and have seen too many cases of swollen batteries. Essentially, it's due to uncontrolled internal pressure: excessive charging current electrolyzes water into a hydrogen-oxygen mixture, causing the casing to bulge when the pressure exceeds its tolerance. The most common cause is a faulty voltage regulator in the alternator, which raises the voltage from 14V to 18V, leading to overcharging. A common mistake among modified car enthusiasts is installing a subwoofer without upgrading the alternator, causing the original electrical system to operate under prolonged overload. Winter requires extra caution, as electrolyte freezing and expanding at -20°C can also be dangerous. Last week, a car had its battery terminals reversed during a jump-start, and the instantaneous current turned the battery into an oval shape like a football.

[BethanyLee]

Three Sins of Battery Bulging: First, overcharging - be alert when the voltage tester shows the red zone; second, high temperature - parking in shaded areas during summer can extend lifespan; third, end of life - ordinary lead-acid batteries age in three years. Once saw an owner using a low-quality charger to revive an old battery, ending up with a pufferfish-like bulge. Internal short circuits are even scarier - a perforation in a cell can generate massive gas. Haphazard wiring in circuit modifications most easily triggers this. A colleague's car fridge wiring melted, causing a short circuit that made the battery swell like bread.