Car battery —  is quite sensitive device to the nature of exploitation and temperature conditions. Negligent exploitation and lack of service leads to a significant reduction in battery life. For example, in the winter in a discharged battery, the electrolyte can simply freeze because of its low density. In the summer, most often another attack. The battery «boils.» Here you should immediately decide on the motions. Under the «boiling» of electrolyte in the battery is understands the process of hydrolysis of water, that is, its decomposition into oxygen and hydrogen. The reasons for this boiling of the electrolyte indicate a malfunction in the on-board electrical system of the machine.

Causes of boiling of electrolyte

The reasons for the battery boiling on the machine may be the following:

  • Overcharge
  • Incorrect exploitation
  • Short circuit of plates
  • Heat

So, it can happen because of different reasons. The reason can be in the faulty elements of the machine, the battery failure and the wrong actions of the car owner. Let’s consider the reasons more.

Why does the car boil the battery and how to avoid it?

Battery overcharge

The main reason of overcharge on the machine is a faulty voltage regulator in the on-board network. As you know, the voltage from the generator depends on the current RPM and varies in time. Therefore,  relay — regulator stabilizes the voltage in the network. Ideally, the voltage applied to the battery should be 12.9-13.4 volts. In practice, for most machines, this value is in the range 14-14.3 volts. The large values are reason for diagnostics.

If the generator is worn or defective, the voltage will be below the specified limits. Then the battery will not be fully charged between the engine starts. If the voltage is higher than the set limits, the process of hydrolysis of water is sharply activated in the battery. As they say, the battery is boiling on the machine.

That`s why, periodically value should be checked with a multimeter on the battery terminals. If the voltage exceeds 14.3 volts, then the battery life begins to decline rapidly. If the voltage is higher than 14.6 volts, then you can not operate the battery in this car. Need a diagnosis and repair.


Incorrect operation

Often there is such situation: The owner of the car turns on a multimedia system, heating and other consumers at the muffled engine. As a result, the battery is very discharged, and then, when the engine is started and the electrolyte is in motion, the battery is boiling. This is due to the fact that the voltage from the generator to the discharged battery is much higher than to the charged one. Therefore, the discharged battery should be recharged by a charger with a voltage 10% of the rated capacity.

Another mistake is often happens with trucks. The buses, special machinery and trucks often use 2 batteries. But at the same a common mistake — installation of batteries with different capacities or lifetime. If they are charged with a mutual voltage, it can cause a situation where one battery is not charged yet, but another one is already overcharged and the battery is boiling.


Short circuit of plates

Another reason for boiling battery, may be malfunctions of the accumulator. There are situations when as a result of a short circuit, one of the batteries (cells) breaks down.

Then, the total battery voltage reduced by the voltage of the individual cell (2.1 volts). As a result, instead of 12.6, we have 10.4 volts. As a result, the voltage of 14 volts from the generator is much higher than the value required for the charge. And the electrolyte in the remaining cells is boiling.

A short circuit can caused by various reasons:

  • Breakthrough of the separator envelope and short circuit of the negative and positive plates;
  • Detachment electrodes from the connecting bridge;
  • Shedding of the active mass of the plates. Gathering at the bottom of the case, they close the plate.

You can diagnose the failure of the accumulator cell by measuring the density and voltage. These indicators will be significantly different from other cells.



This problem occurs in the summer. In a hot period, the temperature under the hood with a warmed-up engine can reach 220 degrees. For battery, the operating temperature is not more than 120 degrees. As a result, the distilled water simply evaporates and the electrolyte level decreases.


Consequences of boiling electrolyte in the battery

The harmful effects of boiling electrolyte exist for both the battery itself and the surrounding nodes under the hood. During electrolysis of water or evaporation, the electrolyte level decreases and its concentration changes.

This affects the performance and characteristics of the battery. In particular, the sulfation of plates increases and the capacity of the battery decreases.

If the battery is not regularly monitored, the electrolyte level may fall below the plate level. In this case, operation is highly Not recommended, as its service life is drastically reducing.

When battery is boiling, electrolyte vapors are rising on the surface of the body. As a result, oxidation of the current leads begins. If the electrolyte is on the lid, dirt, dust and oil immediately sticks to it. A current-conducting membrane is formed, what increases the self-discharge of the battery. So, the harmful processes with the battery grow in an avalanche. And then you puzzle over why the battery is quickly discharged.Why does the car boil the battery and how to avoid it?

That`s why, it is not recommended allowing electrolyte in the battery boiling. What should be done in such a case?


What to do if the battery is boiling?

Take action, depending on the cause of boiling electrolyte. If this is an overcharge of the battery on the machine, voltage regulator or generator should be put in order. For this, you will have to contact a car electrician. Voltage regulators are mechanical, electromechanical and electronic. Depending on what kind of car you have, specialists will replace it or regulate.

Generator breakdowns usually boil down to burn out of diodes, wear of brushes. Depending on the breakdown and condition of thr generator, it is either restored or replaced. During operation, it is necessary to periodically check the voltage produced by the generator.

If there is a malfunction in the battery itself. Let’s say that the battery is boiling due to a short circuit in one of the cans. Then you need to change the battery. If the battery is still new, then it can be delivered under the manufacturer’s warranty. If the warranty period is over, then, most likely, you will have to buy a new one. Restoring the car battery with short circuit of cells is extremely difficult on modern batteries.

At a high temperature under the hood and evaporation of distilled water in the summer, try to check the electrolyte level more often. Top up with distilled water as needed.