What are the reasons for car battery bulging?

car battery bulging

A less common problem with car batteries is their bulging. Some lead-acid batteries, including those with gel, usually bulge, but they will not compromise their ability to operate under optimal parameters. But in other cases, if necessary, you need to check and repair the problem of the inflatable battery. The cause of car battery bulging usually depends on the season. In winter, the battery bulges due to the freezing of the electrolyte, and in summer, the battery bulges due to the formation of gas by boiling.

In both cases, the bulge battery can be repaired, but it is not always a good choice, because in most cases, the capacity of the car battery in normal operation will be reduced, and the best solution to this problem is to replace it. It uses new batteries.

Why does car battery bulging happen?

• Manufacturing defects;

• Condensed or frozen electrolyte that has lost its density;

• Damage to the battery case due to impact or mechanical stress;

• Short circuit between the positive and negative plates;

• The battery is not charged properly. High current or long charging time;

• The voltage regulator in the alternator is damaged or malfunctioning.

In most cases, the electrolyte is the culprit for car battery bulging, either freezing or boiling. They can be raised on one or both sides. The bad thing is that if the battery has a warranty period, it is likely that it will not be replaced without cost, because it is considered a violation of operating conditions.

bulge battery 1

Why do car batteries bulge at low temperatures?

As mentioned above, in the cold season, the battery will bulge due to the freezing of the electrolyte. When it freezes, the volume of liquid will increase, causing the side of the battery to bulge.

The normal freezing point of the electrolyte is -60°C or -76°F. If the density of the electrolyte drops to 50% of the battery capacity, the liquid will freeze at -24°C or -11.2°F. If the battery is almost completely discharged, the battery may have expanded between -7°C to -10°C or 19.4°F to 14°F.

In winter, as the temperature drops, the decrease in density is natural. In addition, because we turn on the heating system and use the lights more frequently in the cold season, the charging is insufficient. Therefore, it is important to control battery power and electrolyte density in winter.

Why do car batteries bulge at high temperatures?

During the electrolysis process, hydrogen and oxygen are released inside the battery. The intensity of gas formation depends on temperature. For those gases to be eliminated, use an exhaust system.

Therefore, the battery bulges because these gases are not eliminated. Here, the exhaust system is the culprit because it is blocked by dust, dirt or impurities. Another reason may be the active formation of gas due to high temperature or malfunction.

summer heat can affect car battery 2

Why does the gas process inside the battery change?

• The battery board is short-circuited.

• The battery charging current is too high.

• The battery is overcharged due to a malfunction of the alternator voltage regulator.

• Overheating can cause the electrolyte in the battery to boil.

• The exhaust system is blocked.

Can a bulge battery be repaired?

Although there are some fixes for this problem, they are not recommended. If the battery body breaks or the plates are damaged, then the only solution is to buy a new battery.

For frozen electrolyte, defrosting and charging the battery can eliminate car battery bulging. To do this, you need to place the battery at a room temperature of approximately 19-22 degrees Celsius or 66-73 degrees Fahrenheit.

Put the battery there until it is completely hot, and charge the battery with a low current, no more than 10% of the battery capacity, for example, 6 ampere is a 60 ah battery.

If the electrolyte boils at the beginning of charging, it indicates that the battery plate is damaged.

The unexpanded battery terminals and the high voltage in the battery wall are signs that the battery may have recovered. Then check the battery to see if it has cracks where the electrolyte may leak.

Then check the battery voltage, it should be about 12.6V, if it is lower than 12, it indicates that the plate is damaged.

You can clean the clogged exhaust port, because the hole is usually blocked from the outside, and you can clean it without removing the battery. In addition, the pressure generated when hydrogen and oxygen come out is not high enough to cause injury or explosion.

But even if you manage to restore the battery after cleaning, charging or defrosting, it will not work as before, so the best solution is to replace the battery with a new one.

How to prevent car battery bulging?

To avoid car battery bulging as much as possible, you need to take precautions, such as cleaning the battery terminals and cleaning the exhaust system. In colder temperatures, avoid battery discharge as much as possible.

If you don’t use the car frequently in winter, the best way is to take out the battery and put it in a warm place. Starting the car frequently is another good way to maintain its function at lower temperatures.

Try to get into the habit of checking car batteries regularly, especially for current leakage. Also, don’t forget the alternator.

Take good care of car battery 3


Car battery bulging is a problem you need to deal with quickly. It is not recommended to continue driving in the presence of this battery problem, as it will damage your car, especially when the acid leaks to your other parts. The best way is to replace the bulge battery, because, as just said above, if you manage to repair it, it will not work as before.

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