How to Charge a Lead Acid Automotive Battery?


With the development of society, a variety of new energy sources continue to emerge, and new energy vehicle has gradually become a new trend in the automobile industry. Because new energy vehicles have solved the problem of air pollution from the root, they have many advantages compared with fuel vehicles. Current technology is not very mature, but the speed of development cannot be ignored. One of the new energy vehicles uses lead acid automotive batteries, but do you know how is a battery charged?

First of all, let’s study the structure of lead acid automotive battery, so that we can know how to charge the batteries better.

Structure of Lead Acid Automotive Battery

Before looking at the different charging techniques, it is important that understanding the battery chemistry and what happens during normal charge and discharge cycles. Normally, the positive plates in a lead acid automotive battery are made from lead dioxide and the negative plates from a sponge lead. The electrolyte is usually sulphuric acid mixed with a gelling agent and is largely absorbed and held by insulating separators between the plates. When a lead acid automotive battery is being discharged, lead dioxide (PbO2) on the positive plate and the lead (Pb) on the negative plate are converted to lead sulphate (PbSO4). Meanwhile, the sulphuric acid (H2SO4) is converted to water (H2O).

In a normal charge, the chemical reaction is reversed. The lead sulphate and water are electrochemically converted to lead, lead dioxide and sulphuric acid. During a full charge cycle any gasses produced need to be re-combined in a so called ‘oxygen cycle’. Oxygen is generated at the positive plates during the latter stages of the charge cycle. It reacts with and partially discharges in the sponge lead of the negative plates. As charging continues, the oxygen produced also re-combines with the hydrogen being produced on the negative plate forming water. With correct and accurate cell voltage control all gasses produced during the charge Guide to charging Sealed Lead Acid batteries cycle will be re-combined completely into the negative plates and returned to water in the electrolyte.


(Structure of lead acid battery)

Stages of Lead Acid Automotive Battery Charging

With the constant current constant voltage (CCCV) method, lead acid automotive battery is charged in three stages, which are constant-current charge, topping charge and float charge.

1. The constant-current charge applies the bulk of the charge and takes up roughly half of the required charge time. During the constant-current charge, the battery charges to about 70% in 5 to 8 hours, and the remaining 30% is filled with the slower topping charge that lasts another 7 to10 hours.

2. The topping charge continues at a lower charge current and provides saturation, which is essential for the well-being of the battery and can be compared to a little rest after a good meal. If continually deprived, the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation.

3.The float charge compensates for the loss caused by self-discharge. It is in the third stage maintains the battery at full charge. The lead acid battery is fully charged when the current drops to a set low level. The float voltage is reduced.  Float charge compensates for self-discharge that all batteries exhibit.


(Stages of lead acid automotive battery’s charging) 

The switch from Stage 1 to 2 occurs seamlessly and happens when the battery reaches the set voltage limit. The current begins to drop as the battery starts to saturate, and full charge is reached when the current decreases to 3% to 5% of the ampere rating. A battery with high leakage may never attain the low saturation current, and a plateau timer takes over to end the charge.

Methods of Charging a Lead Acid Automotive Battery

Charging sealed lead acid automotive battery doesn’t seem a particularly difficult process, but the hard part in charging a sealed lead acid automotive battery is maximizing the battery life. Simple constant current or constant voltage chargers will do the job for a while, but the battery life expectancy quoted by the manufacturers will be reduced by using non-intelligent chargers like this greatly. Maximizing the life of your lead acid battery by using an intelligent charger is not only cost effective, it is also better for the environment. There are different charging techniques, which are very important. Now, let’s show you some methods:

1. Constant Voltage Charging Method

In the process of charging, the charging voltage always remains the same, which called constant voltage charging method, referred to as constant voltage charging method or isobaric charging method. Due to the constant voltage charging from the beginning to the later stage, the power supply voltage is always maintained, so the charging current at the beginning of charging is quite large, which greatly exceeding the normal charging current value. But with the progress of charging, the terminal voltage of the battery increases gradually, and the charging current decreases gradually. When the terminal voltage of the battery is equal to the charging voltage, the charging current is reduced to a minimum or even zero.

This charging method is generally only suitable for special occasions with no distribution equipment or simple charging equipment. When using constant voltage charging method to charge the battery, the power supply voltage is required 2.4 ~ 2.8V approximately for single battery.


2. Fixed Resistance of Constant Voltage Charging

Fixed resistance of constant voltage charging is used to remedy the disadvantage of constant voltage charging. That is, a resistor is connected in series between the charging power supply and the battery, so that the current at the beginning of charging can be adjusted. Sometimes the maximum charging current is limited, so with the charging process, the battery voltage gradually rises, the current is almost a linear attenuation. Sometimes two resistance values are used, with a switch from low to high resistance at 2.4V approximately to reduce air loss.

3. Stage Equal-current Charging Method

The battery in the initial charging with a larger current, then, after a period of time, it changes to a smaller current. Different stages in different current constant current charging method, called the stage equal-current charging method. It can be generally divided into two stages, but also can be divided into multiple stages.

Stage equal-current charging method requires short charging time and good charging effect. Due to the use of small current charging in the later period of charging, it reduces the scouring of active substances by bubbles on the plate and reduces the shedding of active substances. This charging method can prolong the service life of the battery, save electric energy, and charge thoroughly, so it is a commonly used charging method. Generally, the first stage of the battery is charged with 10 hours rate current, and the second stage is charged with 20 hours rate current. The length of the charging time at each stage, the specific requirements and standards of various batteries are not the same.

4. Floating charging method

Lead acid automotive battery is used intermittently or only when AC power is off are charged by floating charging mode. Sometimes using fixed batteries are generally used to charge the battery by floating charging method. The advantages of floating charging method mainly lie in reducing the gas separation rate of the battery and preventing overcharging. At the same time, because the battery is supplied in parallel with the DC power supply, when the electric equipment uses large current, the battery will output large current instantaneously, which helps to stabilize the voltage of the power supply system, and the electricity of the electric equipment is normal. The disadvantage of floating charging method is that individual battery charging is not balanced and charging is insufficient, so it is necessary to carry out regular balanced charging


There are a lot of methods of charging lead acid automotive battery, and there are also many cautions about charging. All the elements will affect using life, performance and efficiency of lead acid automotive battery, so it is significant to know how to charge the battery properly. Otherwise, the battery may become bad or dead because of it.

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