How To Charge A Car Battery & What To Do When It Cannot Be Charged

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Do car batteries need to be recharged? “When, where, and how do I charge it?” Many people may have questions about batteries.

In conclusion, as long as the engine is running normally, the battery does not need to be recharged. However, an exception is made in the case of a dead battery or low voltage.

Therefore, in this article, we will introduce when the battery needs to be charged and how to charge it. It also describes a battery charger for home use, if you are interested.

Does A Car Battery Basically Not Need To Be Recharged?

When you hear the phrase “charging the battery,” you may imagine taking the unit out and plugging it into a power source.

However, cars are equipped with an “alternator” that plays the role of generating electricity and charges the battery while the car is running. Therefore, special charging operations are basically unnecessary.

The alternator uses the engine’s power to move (rotational power) to generate electricity and charge the battery as a backup power source. Even if the car is stopped, the battery can be charged as long as the engine is running.

In other words, it is easy to visualize a car battery by remembering it as a battery that is charged by the power of the engine.

Two Times A Car Battery Needs To Be Charged

The electrical supply from the battery towards the cell motor is essential for starting the engine. Although recharging a car battery is generally not necessary, there are two times when it is required. Since the life of the battery is also involved, it is important to check in advance.

1: When The Battery Runs Out Of Power

When the battery runs down, use a booster cable or a jumping starter to charge the battery externally. Note that the battery discharges naturally, so not only forgetting to turn off the headlights or interior lights, but also not running the engine for a while can cause the battery to run up.

In addition, if the battery frequently runs down, the inside of the battery may be damaged.

As the battery’s storage capacity decreases as it nears the end of its service life, it is a good idea to consider replacing the battery if it has been used for more than two years, if you notice any irregularities around the engine, or if the headlights are dim.

2: When The Battery Voltage Is Low

The standard battery voltage is 12.5 to 12.8 V under normal conditions and 13.5 to 14.5 V when the engine is running. If the battery voltage is below 12.5V, the voltage is low and should be replaced or recharged.

There are also signs that indicate low battery voltage. If you are concerned, check for the following symptoms when idling.

  • Idling stop does not work.
  • Weak sound of revving cell and difficulty in starting the engine
  • The headlights or meter illumination is dim.
  • Wiper and power window operation is sluggish.

When identifying the signs, it is recommended to verify them at night, when electricity usage is higher than during the daytime.

3 Ways To Charge A Car Battery

Car batteries can be charged in three main ways. The battery can be easily recharged anytime the engine is running, so if you are concerned about the amount of charge, try this.

Once A Week, Drive The Car For 20 To 30 Minutes At 50 To 60 km/h.

The battery is charged by the engine’s rotational power, so first move the car at a constant speed. If the goal is to charge the battery, the higher the engine speed, the more efficient the charge.

Those who drive for long periods of time at least once a week are considered to be sufficiently charged on a daily basis. For those who drive less frequently, it is safe to drive for 20 to 30 minutes at 50 to 60 km/h once a week to recover from natural discharge.

Use A Car Battery Charger

If you do not have time to drive at 50-60 km/h for 20-30 minutes every week, we recommend using a car battery charger. Since you can use an electrical outlet at home, you can easily recharge the battery.

The general procedure for using a car battery charger is as follows:

  1. Move the car to an area where a power outlet is available, and prepare a car battery charger and booster cable that matches the voltage of the car.
  2. Open the hood of the car and locate the battery.
  3. Connect the red cable to the positive terminal of the battery and the black cable to the negative terminal.
  4. Turn on the car battery charger and set the charge amperage.
  5. Check the current battery voltage and charge level.
  6. Start charging the battery and confirm that the charge level exceeds 90% (due to the structure of the battery, the charge level does not reach 100%).
  7. When charging is complete, turn off the car battery charger, unplug it from the power outlet, and disconnect the cables connected to it.

Because of the time-consuming and risky nature of the work, first-time users of car battery chargers and those who are not familiar with the structure of the car should check the manual carefully before using a car battery charger.

How to select a car battery charger and precautions for use will be explained in detail in the latter half of this section.

Ask A Service Shop To Do It For You

If you want a safe and smooth recharging process, we recommend that you take your car to a mechanic. Most service shops accept battery replenishment, so you can prolong the life of your battery by requesting this service as part of your regular maintenance.

However, it takes about 10 hours to complete charging, so be sure to request it well in advance.

Tip: In An Emergency, Use Idling Charging

If it is difficult to drive the car, the battery can be charged by idling or idling the car. However, since the engine speed falls below 1,000 rpm while idling, it is safe to assume that you can only charge enough for the next engine start.

When charging by idling, step on the engine until the engine speed exceeds 2,000 rpm while taking noise into consideration.

How To Choose A Battery Charger For Your Car

When preparing a battery charger for home use, check the voltage and type of battery used and select a charger that is compatible.

Check The Compatible Voltage (For 12V And 24V)

There are three main types of battery chargers: 6V, 12V, and 24V. 6V battery chargers are basically for motorcycles, so choose either 12V or 24V for your car. It is common to use 12V for passenger cars and 24V for trucks and buses.

Battery chargers must be used with the correct voltage or risk malfunction and uncharging. If you are not sure about the purchase, it is convenient to buy a type with adjustable voltage.

Make Sure The Battery Is Compatible

Except for hybrid and idling-stop vehicles, lead-acid batteries are commonly used. There are two types of lead-acid batteries: “open type” and “sealed type,” so check which type is compatible before purchasing.

In particular, choose the MF (maintenance-free) sealed type with caution, as there is a risk of expansion and rupture due to rapid charging.

Three Things To Keep In Mind When Charging Your Own Car Battery

The following are three precautions regarding overcharging and explosions when using a battery charger. If you are using a car battery charger for the first time, handle it with extreme caution.

Remove The Battery Before Charging

To prevent damage from spreading in the event of a problem such as connecting the positive and negative terminals incorrectly or overcharging the battery, remove the battery before charging.

However, the act of removing the battery itself involves risks, so please read the car manual carefully and take precautions to ensure safety.

Measure The Charging Time To Prevent Overcharging

If you use a battery charger that does not have an overcharge protection function, be sure to measure the charging time. Overcharging risks depleting the electrolyte inside the battery and shortening its life.

In the worst case scenario, the battery may spark or explode due to the generation of large amounts of hydrogen gas, which is very dangerous.

If there is a greenish solid substance near the terminals, it is due to repeated overcharging, so do not make a judgment on your own, but have a professional service provider perform maintenance.

Open The Cap (Liquid Cap) To Prevent Explosion

Since air bubbles are generated when recharging batteries, the cap (cap cap cap) should be opened. If a large amount of air bubbles are generated inside the battery, the pressure may cause an explosion.

The Japan Battery Manufacturers Association (JBMA) also warns against this risk, so it is recommended to check before charging.

Car Battery Not Charging? Suspected Malfunction And Cause

If the battery does not charge properly, it is suspected to have reached the end of its useful life or to be malfunctioning.

Batteries last an average of two to three years, but this should be considered a rough estimate, as it varies depending on usage. The following is an explanation of two causes of malfunction.

Cause 1: “Battery Failure” Due To Impact Or Overcharging

Even when the battery is installed in the car, there are cases where the electrodes inside the battery are damaged by external shocks.

Think back to whether the battery has ever been subjected to a strong impact, such as in a traffic accident. Short-circuiting due to overcharging or mis-wiring of electrodes can also lead to battery failure.

Cause 2: “Alternator Failure,” Which Causes A Circuit Malfunction

The alternator is the part of the car called the generator, so if it is malfunctioning, the battery cannot be charged sufficiently even if the battery is normal.

Even if the engine turns on temporarily, it is highly likely to get stuck again, so it is recommended to move to a safe place to check it.

If the alternator fails, it will cause strange noises, loss of engine drive power, and the battery warning light will come on. If you have a tester, check if the voltage at the battery terminal reaches about 13.5 to 14 V with the engine running.

If it is difficult to determine the cause of the problem, do not make a judgment on your own, but consult a specialist. Goo-net Pit” allows you to search for the nearest servicing shop that specializes in battery problems. If you have any trouble, please make use of this service.


Normally, a car battery is charged when the car is running, so there is no need to charge it yourself. However, when the battery is running low or voltage is low, the battery should be charged from an external source.

In particular, those who do not use their cars very often are at risk of voltage drops due to natural discharge, so it is advisable to drive for 20 to 30 minutes at 50 to 60 km/h once a week.

In addition, care should be taken in the use of battery chargers. Handle it with care to avoid the risk of overcharging and explosion.

If you are having trouble charging your battery, or if your battery or alternator is not working properly, we recommend that you consult a specialist rather than trying to solve the problem on your own.