How to Charge a Car Battery Correctly so as Not to Ruin Anything

Don’t rush to the store for a new battery if the old one starts acting up. You might be able to save money by simply charging the ailing battery.

The battery may be discharged, but in many cases it can be revived. In this case, you will need not a defibrillator, but other devices that you also need to know how to use.

When to charge the battery

The battery serves as a power source for the starter, which starts the engine, and when the internal combustion engine is turned off, it supplies energy to the car’s lighting and multimedia. But the battery can also run out of power. When does this happen?

• If the battery is new, but more than six months have passed since its production until installation on the car. Then significant self-discharge of the battery is quite likely.

• If the car is not used for more than a month.

• If the service life of a lead-acid battery has exceeded 3-4 years.

• If you leave the car for several hours with the lights and/or music system on and the engine turned off.

• If the vehicle’s electrical system is faulty.

• For frequent short-distance trips and in traffic jams.

How to check a car battery charge

Before waiting for the battery to run down, it is better to periodically check its condition. There are several ways to do this:

A fully charged passenger car battery should have a voltage of 12.6 volts or more. (Photo: Shutterstock)

How to charge a car battery

Let’s leave aside exotic things like powering the battery from laptop battery chargers and consider specialized devices. When choosing them, you should first check:

• Compliance with the battery voltage (12 or 24 V) of your car;

• The ability to produce the voltage required for charging. Thus, some batteries require currents of 16–16.5 V, which not all chargers are capable of.

According to design, there are two types of chargers:

Transformer. Outdated, quite large and bulky devices, but they have an undeniable advantage – simplicity of design and the associated reliability. The average price of transformer chargers is about 60$

Pulse. They are much more compact than transformer ones. In addition, pulse chargers, as a rule, have many protective mechanisms (against overcharging, short circuit, polarity reversal) and a higher degree of automation. It is more difficult for such a device to damage the battery during charging.

The price range for pulse chargers is wide: from less than 40$ to more than 200$ for multifunctional devices that are suitable not only for lead-acid batteries, but also for AGM/Gel batteries.

The warranty period for both types of chargers is usually one year.

When choosing a charger, you should pay attention to whether they have a number of useful functions:

• Desulfation mode. Using charge-discharge cycles, such devices clean the battery plates in a few hours (in advanced cases – days) from lead sulfates formed in the heat and during deep discharges, which reduce the battery’s performance;

• The battery capacity indicator will help you understand how much and how long it took to recharge the battery.

How to charge a car battery

The most common lead-acid batteries are filled with a chemically aggressive liquid electrolyte, which releases flammable gases during charging. Therefore, when working with a battery that involves opening its cans (compartments), it is necessary to follow safety precautions:

• Use protective glasses and gloves.

• Do not smoke near the battery.

• Avoid sources of sparks and open flames near the battery.

• Perform battery maintenance in well-ventilated areas.

The battery charging time depends on its condition and the length of use. (Photo: Shutterstock)

If you follow these rules, it is not necessary to remove the battery from the car during charging – you only need to turn off the ignition and all on-board electrical equipment. However, it is advisable to remove the battery for at least two reasons:

• It is easier to clean a removed battery before charging. You can remove oil and oxides from the terminals with a metal brush, and wipe the case with a rag, dry or soaked in a 10% solution of ammonia or soda.

• If the garage is unheated, then at sub-zero temperatures the battery should be moved to a warm room to speed up charging.

Having decided on the location of the battery charging, we perform the following actions:

1. For serviced batteries, unscrew the can caps to ensure free removal of electrolyte vapors that are intensively formed during charging, and to prevent excess pressure from being created in the battery case. To guarantee the prevention of explosion of unserviced batteries during charging, firstly, check whether the battery gas outlet tube is clogged, and secondly, use devices that automatically maintain the voltage set by the manufacturer and switch off when the battery is fully charged.

2. If the electrolyte level is insufficient, add distilled water to the open cans of serviced batteries.

3. We connect the charger to the corresponding terminals of the battery: the red wire to the positive, the black wire to the negative.

4. We plug the charger into the network. After the operation is completed, the disconnection occurs in the reverse order.

How to charge the battery correctly

There is no consensus on how to properly charge a battery, if only because two methods and their combinations are used for this.

Constant voltage charging

This is how the car battery is charged, so it is considered that this method is the most gentle for the battery. In addition, this method is the simplest. You only need to set the voltage value (usually 14.6-15 V) on the charger.

However, this method allows you to charge the battery no more than 90-95%, requires a significant amount of time (up to a day) and causes strong heating of the battery due to the high current at the beginning of the charge.

DC charging

The method provides a full charge of the battery, which requires about 10 hours when choosing the optimal current strength. Deviations from this value in either direction are undesirable: the result will be either a significant increase in charging time or undercharging.

Unlike constant voltage charging, constant current charging is not a single-stage process and requires control. Initially, the charging current should be numerically equal to 10% of the nominal capacity of the battery (for example, 7.2 A at 72 Ah).

When the voltage at the battery terminals increases to 14.4 V, the current is halved. An obvious disadvantage of this method is abundant gas emission, which can lead to the battery boiling over.

Before waiting for the battery to run out, it’s better to periodically check its condition

Combined battery charging method

The method is based on changing modes. At first, constant current charging is used, and as soon as the battery replenishes its energy reserve by 50–60%, it automatically switches to constant voltage charging mode. Most pulse chargers are designed to use this charging method.

How long does it take to charge a battery

The battery charging time depends on its condition and the length of its use. The first charge of a new battery is the longest (25–50 hours). Heavily discharged used batteries replenish their energy reserves in 10–16 hours. Special online calculators help to roughly calculate the required charging time. You can also use tables available on the Internet as a guide.

Here’s a table based on the information provided:

What to do if the battery boils while charging

The appearance of gas bubbles in the electrolyte of a lead-acid battery being charged, which is commonly called boiling, is not dangerous in itself. This is only a visible manifestation of the beginning of the chemical reaction of electrolysis, which indicates that the battery charge is approaching its maximum. But boiling is not all the same.

1. If bubbles in the electrolyte appear approximately 5-8 hours after the start of charging, the battery is in good condition. In this case, you can continue charging for another 2-3 hours. The automatic charger will automatically determine the moment of disconnection. When charging in manual mode, excessively vigorous boiling is stopped by reducing the charging current. Continued boiling after disconnecting the charger means that the battery has been overcharged.

2. If boiling begins in all or several battery banks almost immediately after connecting the charger, the battery has exhausted its resource.