How to charge a battery correctly (how long, what current and voltage), how to charge a maintenance-free, gel and calcium battery

About, how to charge a car battery Every car owner should know. This is necessary not only to increase the battery life, but also to ensure the safety of the entire automotive electrical system. The answer to the question of how to properly charge a battery depends on several factors, including the type of battery, its capacity, the value of current and voltage for which the battery is designed, etc. You will learn about all this if you read this material to the end.

How to properly charge a car battery

Before moving on to practical tips and recommendations, it is necessary to briefly dwell on theoretical issues. So, batteries are charged in one of two possible ways - using direct current and using constant voltage. Let's consider each of them separately.

DC charging

As the name suggests, a variable charger sets the charging current to 10% of the battery capacity (for example, a traditional 60 Ah car battery is charged at a constant current of 6 Amps). In this case, the voltage value will change during charging.

One of the disadvantages of this method is that it is necessary to periodically (about once every one or two hours) adjust the current value, which can also change. As for old maintained batteries, gas will be released from their electrolyte, and the more charged the battery is, the more intense the gas release will be. By the way, intense release of gas from the electrolyte is one of the signs of a fully charged battery.

Initially, the voltage output from the charger will be relatively low and will increase as charging progresses. At the moment when the voltage reaches 14.4 Volts, it is necessary to reduce the current by half (if it was 6 Amperes, then it must be reduced to 3 Amperes). The charging process must be carried out before intense gas evolution from the electrolyte begins. When the voltage reaches 15 Volts, the current value must be reduced by another half (to 1.5 Amperes in the example given). This must be continued until the voltage reaches a constant value and stops increasing. The second signal that the battery is fully charged will be the fact that the voltage and current values do not change for one to two hours. How long to charge can be calculated using a special calculator:

Constant voltage charging

Another charging method is to set a constant voltage on the charger. This value depends on the type of battery. When the battery is connected to the charger, the current value will be maximum (and it will be greater, the more discharged the battery is). As a rule, chargers have circuit solutions that forcefully limit the charging current to about 20...25 Amperes. This is done to preserve the functionality of both the charger and the battery. As charging proceeds, the voltage at the battery terminals approaches that supplied by the charger, and the current approaches zero. This happens according to the exponential law.

The choice of constant voltage value depends on the degree of discharge of the battery. For example, at a voltage of 14.4 Volts, the battery will be charged 75...85% in one day. At a voltage of 15 Volts - by 85...90%, and at 16 Volts - by 95...97%. To fully charge the battery in a day, you need a voltage of about 16.3...16.4 Volts. Please note that for many modern maintenance-free batteries there is an artificial voltage limit, for example, equal to 14.4 Volts. Under such conditions, it will take more than a day to fully charge the battery.

How to charge a car battery

Regardless of the type of battery, to charge it, you must use a source of constant current (constant voltage) with the ability to adjust these values. It is best to use special chargers for this, sold in car stores or markets. It is important that a charger designed for charging a battery designed for 12 Volts DC makes it possible to increase the charging voltage to 16...16.5 Volts. This is necessary in light of the fact that otherwise it will be impossible to charge a modern maintenance-free battery to its maximum capacity (100% of its capacity).

Battery (car battery)

A car battery is a vehicle's energy source that is responsible for starting the engine. The main faults are sulfation, terminal oxidation, short circuit. It is checked with a multimeter and charged with constant current or voltage. More details

First, let's consider the simplest type of battery - “antimony” (antimony is added to the plate material) and “hybrid” (antimony, calcium, and sometimes silver are added to the plate material). Accordingly, a regular charger is suitable for charging them. The charging current must be selected depending on the battery capacity, it must be 10% of its value (for example, a battery with a capacity of 60 Ah must be charged with a constant current of 6 Amps). The constant voltage value should be in the range from 13.8 to 14.5 Volts. During the charging process, the current value will drop, and this will happen according to an exponential law. This fact is also the answer to the question - how long to charge the battery. Accordingly, the duration of the loading process depends on several factors:

battery capacity;
the degree of its discharge;
charger power;
general technical condition of the battery.

The higher the charging current, the faster the battery will charge. However, in this case the probability of its discharge will also be higher. Therefore, many car enthusiasts set the current value to around 2 Amperes (approximately, depending on the capacity), and leave the battery with the charger overnight (about 6...10 hours). This approach will eliminate “overcharging,” which is very harmful to the battery, and will also provide better charging (in the future, the battery will retain its charge longer).

Please note that before the charging process, it is advisable to clean the battery terminals from plaque and rust (if any), even for preventive purposes. This will ensure better electrical contact. And after charging, it is advisable to treat the battery terminals with special means for this.

The battery charge level must be monitored regularly and the corresponding value must be checked at least once a month. Moreover, this does not depend on the time of year or the ambient temperature, although it is in the cold that problems with the battery arise much more often.

Before the charging process, it is necessary to unscrew the caps on each of the cans (for batteries being serviced), and also remove the plug in order to ensure the free release of electrolyte vapors and not to create excess pressure inside the battery. After removing the plugs, you need to check the electrolyte level in each jar. If its level is low, you need to add distilled water until it completely covers the battery plates.

Features of car battery maintenance

A set of instructions for proper maintenance of different types of car batteries. Features of servicing gel, alkaline and acid batteries Read more

It is not advisable to charge serviced batteries at home, since during the process of boiling the electrolyte, gas is released that is harmful to the human body (in high concentrations it is explosive). Accordingly, it is advisable to charge in a garage or in well-ventilated areas. As for maintenance-free batteries (the caps on the banks cannot be unscrewed), they can be charged in the apartment, since similar gas is not released under normal charging conditions.

What happens if you charge with high current?

Some car enthusiasts, in order to save time, charge the battery with a high current. This error can occur if you turn on the battery, set it to a certain value and stop monitoring the process, for example, leave the garage. As the density of the electrolyte increases, the current may increase excessively.

First of all, high current can lead to failure of the charger, even to the point of ignition. Therefore, it is impossible to install starter-chargers on easily flammable tables and stools.

At high current, the temperature of the electrolyte increases. It may boil. If the electrolyte boils, water evaporates first. Concentrated acid remains in the jars, which destroys the plates. This way you can completely lose the battery.

The most terrible consequence of high current is the explosion of a battery bank. More than one battery worker received chemical burns as a result of a battery explosion. Therefore, it is necessary to stop the operation immediately if the electrolyte boils!

When to charge the battery

Before charging the battery, you must ensure that it is truly discharged. There are several ways to do this:

Measuring voltage at terminals . This can be done using a constant voltage voltmeter, in other words, an electronic multimeter or a pointer tester. For standard batteries used in most passenger cars, the standard voltage value is 12 V. In practice, it differs slightly from the nominal value. So, a value equal to 12.7 V tells the car owner that the battery charge level is 100%, and accordingly, there is no need to charge it. If the measured voltage is 12.2 V, then this indicates that the charge level is approximately 50%. And if the voltage drops to 11.6...11.7 V, it means that the battery is almost completely discharged and it needs additional charging.
Measuring the electrolyte density value . However, this verification method is only possible for so-called serviceable batteries, that is, in which it is possible to reach containers with electrolyte (and add it, if necessary). To measure density, a special device is used - a hydrometer. The electrolyte density should be around 1.27 g/cm³. If it is significantly less, it means that the battery should be charged with a charger. In unattended ones there is a special window where 3 stages of density will be displayed.
Problems starting the engine . One of the reasons why the starter does not turn, and problems arise with starting the engine, is precisely the battery discharge. This is usually accompanied by problems in the operation of other consumers of electricity in the car - lighting, operation of the audio system, and so on.

In a discharged battery, sulfation of its lead plates occurs, which leads to a sharp decrease in its service life, that is, durability.

The basic principle of charging current control

There are two main principles:

Do not exceed the maximum current equal to 1/10.
Do not set the initial value below 1/20 of the battery capacity.

Applying electric current to the terminals causes a complex chemical reaction in the electrolyte and on the surface of the lead plates. When the process proceeds moderately, they gain a full charge without being exposed to danger.

Exceeding the required level causes too violent a reaction. Several such charges can simply destroy the plates.

Low current is also harmful. In this case, only the outer layer of the plates will be charged. After which the charging current will drop to zero, and the voltage will increase to the specified value. It would seem that the battery is charged. But that's not true! The plates become sulfonated, do not take on a charge and become passive.

In both cases, the battery will have to be thrown away.

Is it possible to charge the battery in a car?

Many car enthusiasts, especially beginners, are interested in the question of whether it is possible to charge the battery without removing it from the car. It is important to separate concepts here. As for its physical removal (for example, moving it closer to the charger), charging can be carried out directly on its seat. However, if we are talking about disconnecting car terminals, then this must be done! You especially need to disconnect the negative terminal, although both are better. This is due to the fact that even in a situation where the engine is not started, the electric current from the battery still passes into the electrical system of the car, powering the corresponding elements.

Firstly, during charging, some of the electrical energy from the battery will go into the system. This will naturally increase charging time. Secondly, there is always a risk of a power surge or other similar troubles, which can negatively affect the condition of the elements of the car's electrical system. This is especially true for expensive cars (business and premium class), the design of which has a lot of built-in electronics. She will be at risk.

Maximum battery charging voltage

We know that modern high-class cars have an on-board system that runs on 16 V. What batteries are used in these batteries? To avoid gas emissions, the system must be closed.

This means that maintenance-free Ca/Ca batteries can withstand harsh operating conditions. They use a special charging mode. Using calcium instead of antimony allows the battery to be charged at higher voltage, which causes the electrolyte to boil. A maintenance-free battery does not tolerate sudden changes in voltage in the on-board network. It is designed for vehicles with a good electronic voltage control system. Hybrid batteries made from low-antimony and calcium plates are more tolerant of operating conditions.

How to charge a calcium battery

Calcium batteries (also designated Ca-Ca) are practically maintenance-free and are relatively new devices on the automotive market. They have many advantages (high starting currents, significant capacity, the electrolyte does not evaporate from them), but they also have disadvantages. One of them is that if they are charged incorrectly, then after 3…4 deep discharge cycles their capacity decreases significantly. Accordingly, the charging process is critically important for them.

Since calcium batteries are made using a special technology, their charging process is special. So, for this it is necessary to use chargers capable of delivering direct electric current with a voltage range of 16.1...16.5 Volts. Accordingly, if any power supply produces a maximum voltage value of 14.8 Volts, and then the electronics “cut it off”, then in this case the battery will be charged to 45...50% of its capacity. If the same value is 15.5 Volts, then charging will occur at 70...80% of the capacity. Accordingly, you will never reach a normal 100% charge (an excellent charger for charging calcium batteries is the Orion Vympel-55 with a programmable cycle).

It is interesting that the electric generators of modern passenger cars are not able to produce such a high voltage. Usually it does not exceed 15 Volts. Accordingly, a calcium battery cannot be charged when installed in a car. The generator simply does not allow it to discharge. However, given the harsh domestic winters, cold and harsh operating conditions can do their dirty work and discharge the calcium battery. Therefore, it needs to be recharged periodically (about once a month)! However, to do this you need to have a charger with programmable modes. You need to recharge according to the following algorithm:

Set the voltage on the charger to 16.1 Volts. The current value will be equal to 10% of the battery capacity (for example, if the battery capacity is 60 Ah, then the current value will be 6 Amperes).
In this mode, you need to charge the battery until the charging current drops to 0.5 Ampere. This can take a few minutes or several hours, it all depends on the discharge of the battery, its capacity and general technical condition.
Set two modes. Upper - voltage value 16.1 Volts and 3 Amps. Lower - 13.2 Volts and 0 Amperes.
Arrange a so-called “swing”. Their meaning is that at a current of 3 Amps the voltage value gradually increases to a value of 16.1 Volts. When this value is reached, the current disappears (equal to zero), and the voltage smoothly drops to 13.2 Volts. Next, the current is again set to 3 Amperes and the voltage again rises to 16.1 Volts. Then everything is repeated.
As the battery charges, the time intervals for switching modes will decrease. Initially, the process of voltage increase will take several tens of minutes, and the decrease time will be very fast. However, over time, the opposite situation will occur. That is, a voltage drop to 13.2 Volts will last for minutes, and its increase to 16.1 Volts will take less than one minute. This situation indicates that the calcium battery is fully charged.

What voltage should I set when charging the battery?

Voltage is a potential difference, and the current will flow in the direction where this value is smaller. Therefore, the charger voltage is always selected higher than the charging level of the car battery. The greater the voltage difference, the faster and more fully the car battery will gain capacity after charging.

During charging at a constant voltage, the limit of the parameter set on the charger is lower than the characteristic at which the release of gases from the battery being serviced begins. What potential difference is needed to charge a car battery? The maximum voltage used when charging the battery is 16.5 V. Which parameter should be depends on the type of battery. The time and completeness of battery charging depends on the voltage. The ratio of charge voltage and capacity recovery for a 12 V battery in 24 hours is as follows:

With a voltage of 14.4 V you can charge the battery by 75-80%;
Using a voltage of 15 V, the charge level is 85 - 90%;
With a voltage of 16 V, the battery is charged by 95 - 97%;
With a maximum voltage of 16.3 -16.5 V, the batteries are fully charged.

When the battery voltage reaches 14.4 - 14.5, the charging end signal lights up on the charger.

It has been established that it is this voltage of the car battery that does not create gas emissions after and during charging. Therefore, during actual vehicle operation, the generator, through a voltage regulator, limits the maximum voltage level to this value. In summer this figure is close to 100% capacity, in winter it corresponds to 13.9-14.3 V, with the engine running, which corresponds to 70-75% capacity.

How to charge a gel battery

Gel batteries are another type of modern battery that has advantages over traditional acid batteries (they are designated GEL). Basically, they are used as power supply for car multimedia systems and batteries for scooters, motorcycles, and ATVs. They can also be used in uninterruptible power supplies (UPS) for computers, gas boilers and other household appliances. The advantages of gel batteries include:

high current output, even in low charge mode (about 20...30% of the nominal value);
a large number of recharge cycles (up to one thousand or even more, depending on the specific model and operating conditions);
minimum self-discharge current (this allows you to keep the battery in a charged state for a long time, even in unfavorable operating conditions for it, it can only lose about 20% of its charge per year!!!);
The gel battery can be stored completely discharged even at negative ambient temperatures.

As for the disadvantages, gel batteries have only two of them:

high price compared to traditional acid batteries with the same technical parameters;
A gel battery really does not like increasing voltage (overcharging), and under such conditions its capacity is significantly reduced and the overall service life is reduced.

Many car enthusiasts who use such batteries are interested in the question of how to charge a gel battery? In fact, there are few differences from charging traditional batteries.

For charging, a conventional charger is used with the ability to adjust the value of the current and voltage it produces.
The current value is selected depending on the battery capacity. It should be 10% of it. For example, for a battery with a capacity of 60 Ah, the charging current should be 6 Amperes. In extreme cases, for example, if you need to charge the battery quickly, then it is allowed to take 30% of the capacity. That is, in our case it will be 18 Amperes.
For a gel battery, it is important not to overdo it with the voltage value, that is, you should not set its value too high. As a rule, the limit value in this case will be 14.5...15 Volts (additional information should be checked on the sticker on the battery case).
The maximum value of the permissible charging current is designated as max initial current . The charging current must not be allowed to increase above the corresponding value.
The charging time of a gel battery depends on the charging current. To calculate it, you need to divide the capacitance value by the current value. If the current was chosen at 10% of the capacity, then the charging time will be the same 10 hours. If the current is lower, then the time will be longer. In order to exclude the possibility of overcharging (which is very harmful for a gel battery!) it is better to use special electronic chargers for this, which will automatically select both the charging current and the time period for this.

The reason that the battery is destroyed when the voltage increases is that under these conditions the gel, which acts as an electrolyte, begins to melt. And the higher the voltage, the stronger the melting. And the longer the time of excessive recharging, the worse it is for the electrolyte gel.

If the gel battery is serviceable, then it is necessary to unscrew the plugs from its cans (containers) so as not to create excess pressure inside it. The charger probes must be connected to the corresponding terminals on the battery (observing polarity). Next, you need to set the appropriate current and voltage values on the charger. As the battery charges, the voltage in it will increase. It should not be allowed to go beyond the cycle use . If this happens for a short time, then you need to reduce the current in order to reduce the voltage. Under such conditions, the battery can usually be fully charged in 10...12 hours.

Often the label will indicate a Standby Use , which indicates at what voltage the battery can be in standby mode. The manufacturer implies that the battery can be stored for a long time without recharging, but to maintain its performance without load, it must be periodically recharged with a low voltage. Typically this range is around 13.5...13.8 Volts. Failure to comply with this requirement will lead to irreversible consequences, in particular, rapid loss of battery capacity and rapid failure.

The optimal solution for charging a gel battery is to use special electronic chargers that will automatically control the value of the charging current and voltage, and, if necessary, limit them. In addition, such chargers select the charging mode based on the degree of discharge of the battery, as well as external factors such as ambient temperature. There are chargers on the market that are specifically designed to work with gel batteries. In particular, they have a temperature compensation function and a function for controlling the charging process in stages in automatic mode.

Please note that if a gel battery is installed on the machine, then it is imperative to periodically check the functionality of the voltage relay on the generator. If it fails, the battery can fail in literally a matter of hours. You can buy terminals with a relay regulator as additional protection.

Charging time at 60 Ah

Charging time is selected individually depending on the device being used. First you need to understand whether the battery is completely discharged or not.

If we exaggerate and imagine that the battery has completely lost its charge, and there is a current strength of 10% of the nominal value, then it will take 10 hours to fully charge the battery.

If the voltage is adjustable, then we use 4-5 hours for a 90% charge and 8 hours are required for a 100% charge.

All values are at maximum discharge. If the battery is only partially discharged, then the time must be adjusted.

How to charge a hybrid battery

In hybrid batteries, one part of the plates is made using “antimony” technology, and the other is made using “calcium” technology (sometimes with the addition of silver). The battery is low maintenance, but it still has plugs. Accordingly, it is necessary to check the electrolyte level once every two to three months and, if necessary, add distilled water to it. Among the advantages, it is worth noting its resistance to deep discharge and the ability to produce high starting current. As for the price, it is acceptable, and approximately two times less than calcium.

As for the charging process, it is standard and not difficult. So, it is necessary to charge with a current whose value is 10...30% of the capacitance value. As mentioned above, for 60 Ah the current should be 6 Amperes (if you need to charge faster, you can increase it to 18 Amps). It would be optimal to set the current value to 2 Amperes. The voltage value will be in the range of 13.8...14.2 Volts. The charging end signal will be a voltage value of 14.2 Volts and a current value of 0.3...0.5 Amperes.

You cannot set high charging currents, otherwise the electrolyte will boil, which is extremely harmful for the battery plates; they heat up and the active mass may fall off from them.

A special feature of a hybrid battery is that in the summer it is necessary to regularly check the electrolyte level. This is due to the fact that, unlike its old “brothers”, such a battery produces a higher operating voltage. And if in winter this only helps to start the engine without problems, then in summer it turns into free energy. This is fraught with the fact that the electrolyte may boil and begin to evaporate, and the acid concentration increases. Because of this, the plates heat up and become exposed, thereby becoming damaged. Therefore, in the summer, in addition to recharging, it is necessary to monitor the electrolyte level in the hybrid battery banks.

Dependence of battery charging on voltage

Each type of battery is charged based on the characteristics of the types of designs used. Serviced, gel and lithium batteries have the lowest charging voltage. Causes: boiling over, destruction of the composition, fire hazard. If the battery being serviced can be charged with a simple charger, lithium and gel systems require compliance with a 2-stage combined energy storage mode.

All systems are designed to prevent overcharging and are equipped with automatic power off when the voltage required for a car battery is reached. When charging, the current gradually decreases due to an increase in resistance, but the voltage remains stable. After charging, the electrochemical reaction process continues in the form of a slight self-discharge.

It is important that the charging voltage always exceeds the parameters required for operating the device. For current to flow, you need a slope, which is the voltage difference between the charger and the battery.

How to charge an AGM battery

New batteries made using AGM technology are confused by many car enthusiasts with gel batteries (denoted as GEL). In fact, these are two different types of batteries. One of the advantages of such batteries is high starting currents (up to 500...900 Amperes), which allows you to start any engine in cold weather without any problems. Another advantage of an AGM battery is faster charging (about three times faster). And it charges perfectly from a car generator. And its service life is 3...5 years longer than that of a conventional acid battery.

As for charging AGM batteries, there are three options. In particular:

Charge, accumulation, storage . The charging process can be carried out directly on the car or using a charger. In this case, the voltage value will be in the range of 14.2...14.8 Volts (but not more than 15.2 Volts, you need to further clarify in the instructions), the current strength will be 10...30% of the capacitance value. Energy is accumulated after deep discharge. The voltage is similar - 14.2...14.8 Volts, and the current is 10% of the capacity (no more!). In storage mode (for example, long-term storage in a warehouse or garage), the charging voltage should be within 13.2...13.8 Volts, and the current value should be 5...10% of the capacity value.
Charging and storage . This is the most common option and is recommended by most manufacturers. For charging, the voltage is 14.2...14.8 Volts, and the current is 10...30% of the capacity. For storage, the voltage will be 13.2…13.8 Volts.
Loading . Some manufacturers do not indicate the storage mode, but only provide information about charging conditions. They are identical to those given above - the voltage is 14.2...14.8 Volts, and the current is 10...30% of the battery capacity.

A few words about chargers. As with gel batteries, current and voltage levels must be closely monitored. Therefore, it is advisable to purchase an electronic charging unit in advance, preferably with two modes. This will not only minimize the participation of the car owner in the charging process, but will also ensure safe and efficient charging. If you decide to buy a mechanical charger, you will need to manually carefully monitor and adjust the current and voltage values.

What is a car battery?

Car batteries are types of electric batteries. They are used on cars and motorcycles. Its purpose is as follows: starting the engine, serving as a power source in the vehicle’s on-board system when the engine is turned off. It also plays the role of a voltage stabilizer for the vehicle. The most common are 12 volt batteries. They are found on cars, mini buses, and also on lightweight trucks. Batteries with a voltage of 6 volts are built into motorcycles. And the 24 volt battery is installed in heavy trucks and military equipment.

car battery

To start the engine, the battery must crank, which is provided by the starter. It receives power from the battery. At such a moment, it uses a lot of energy, thereby discharging the battery itself. Once the car starts, the power supply goes to the generator. The scheme is this: driving a car recharges the battery.

How to charge a maintenance free battery

Many modern batteries are maintenance-free. This means that they cannot check the electrolyte level and the condition of the plates. In general, the process of charging maintenance-free batteries is not much different from a similar procedure with old batteries. Charging can be done with either constant current or constant voltage. The best option would be to use an electronic automatic charger for this, for example, with a charging indicator light (a green light indicating the end of charging). It will not only make the car owner’s work easier, but will also ensure the correct current and voltage values, as well as charging time.

However, if you use a mechanical charger, then calculating the charging time is important in this context. To do this, you need to calculate the degree of its discharge. A voltage value at the battery terminals of 12.7 Volts indicates a 100% battery charge. If the same value is equal to 11.7 Volts (it could be lower, but this will already be a deep discharge, which is harmful for many batteries), then it can be taken as 0%. Accordingly, for example, a voltage of 12.2 Volts will indicate a charge of 50% capacity.

The optimal charging current is 10% of the capacity. In the example repeatedly given above, this would be 6 Amps for a battery with a capacity of 60 Ah. For example, if the measured voltage at the terminals is 12.2 Volts, that is, the battery is 50% discharged, then this means that to fill its capacity we need to supply 30 Ah. Therefore, 30 Ah must be divided by the current value of 6 Amps, resulting in 5 hours. Theoretically, you can apply all 30 Amps to reduce the time to one hour. However, this should not be done as it will kill the battery. And you will have to change it sooner than you would like.

It is important to understand that overcharging is harmful for any battery. That is, for example, what will happen if you wait not 5 hours, as in the previous example, but 7 or 10? In this case, the level of capacity and charging will not change, but the process of boiling of the electrolyte will begin with its evaporation. And if it can be topped up in a serviced battery, then this cannot be done in an unserviced one; accordingly, such a situation cannot be allowed either! The boiled electrolyte will evaporate through the safety release valve when critical pressure is reached inside the battery cans. However, its body will remain intact (it will not explode, as many car enthusiasts think). But a low electrolyte level will reduce the battery capacity and reduce its overall operating life. According to the instructions, recharging is allowed for a maximum of 15...30 minutes.

Lead battery charge current

Different chargers are used to charge batteries with lead plates, but the main task when charging a battery will be how to calculate the battery charging current and how to limit the charging current in order to prevent the plates from falling off and the electrolyte from boiling. This is why pulse chargers are used, which do all the work automatically.

Chargers with manual adjustment of parameters, in particular charging current, require constant monitoring of the process in order to change the charging current characteristics in a timely manner. Current, charge time and voltage are the main parameters that will have to be controlled when charging manually or they will be regulated by a pulse charger. Calculating the rated charge current is quite simple. To do this, you need to know the capacity of the battery, and the charging current should be one tenth of the nominal capacity of the battery.