What Causes Car Battery Bulging?
4 Answers
Car battery bulging is caused by: 1. Issues with battery manufacturing quality, such as uneven electrode coating and rough production processes; 2. Intense short-circuit reactions generating excessive heat, leading to electrolyte decomposition and vaporization; 3. Prolonged battery inactivity. Car batteries, also known as storage batteries, are a type of battery categorized into standard batteries, dry-charged batteries, and maintenance-free batteries. Their working principle involves converting chemical energy into electrical energy. The functions of a car battery include: 1. Providing starting current to the starter when starting the engine; 2. Assisting the alternator in powering electrical equipment when the generator is overloaded; 3. Supplying power to electrical devices when the engine is idling; 4. Protecting the electrical components used in the vehicle.
I've been driving for decades and have seen many cases of swollen batteries. The main cause is overcharging—like when the voltage regulator fails, and the charging voltage exceeds 15 volts, causing the electrolyte to decompose and produce a large amount of gas, which bulges the casing. High temperatures are another culprit; in summer, engine compartment temperatures can reach 70-80 degrees Celsius, making thermal expansion particularly noticeable. My old car battery once had a big bulge on the side due to this. Another often overlooked issue is low battery fluid levels, where the plates are exposed, causing intense bubbling during charging. Nowadays, I always advise my friends to regularly check the charging system voltage, clean the battery vent holes before summer each year, and avoid using cheap, low-quality chargers to save money.
Last time I went to replace the battery, I found the old one swollen like a pufferfish. The mechanic said this is most common in electric vehicles that frequently undergo deep discharges, such as regularly using up the battery below 20% before recharging. In such cases, lead sulfate crystals accumulate on the plates, causing a sharp temperature rise during charging. Another scenario is using the wrong charger in winter—low-temperature-specific chargers with inaccurate current control can fail to compensate for temperature during charging. The swollen battery in my car was caused by rapid charging at -20°C last winter. Now I know it's essential to preheat the battery before charging in cold weather to avoid sudden voltage spikes. Recently, I installed a Bluetooth battery monitor to keep an eye on temperature and voltage in real-time, which makes charging much safer.
Upon opening the swollen battery, it was observed that the internal gas had deformed the casing. The root cause of gas generation is overcharging and overdischarging. When the charging current exceeds three times the rated value, the electrolyte decomposes exceptionally rapidly. A blocked safety valve is even more problematic—just the other day, a repaired vehicle had its charging port completely clogged with dirt, preventing the vent from releasing gas. Additionally, overly tight battery mounting brackets pose a hidden risk, as there's no room for thermal expansion and contraction. It's recommended to check the battery frame for looseness every three months, leaving a 5mm expansion gap. Installing a voltage regulator is essential, with 14.4 volts being the safest upper limit.
