How to Charge a Bosch S4 Battery

In this article we will talk about maintenance-free batteries and how to properly charge them.

Technological progress does not stand still

Even 10-15 years ago, motorists had to regularly maintain the battery (check the density of the electrolyte, top up with distilled water, and so on).

At the present stage, serviced batteries are a thing of the past. In their place came the more modern and reliable (according to the manufacturers) unattended power sources.

All that is required from motorists is to control the voltage level and charge in a timely manner. The only question is how to do this job correctly.

What are the differences between serviced and maintenance-free batteries?

Today, all power sources can be divided into two types:

The first batteries served were lead-calcium type. Their main advantage is the ability to work for two years without adding electrolyte.

But there was also a minus. a deep discharge turned out to be "deadly" for the battery. Only a few charge and discharge cycles, and the battery could be carried to garbage.

In the late 90s, more modern ones appeared. lead-calcium products. Their feature has become greater resistance to discharges and the lack of the need to top up with distilled water.

At the next stage, lead-acid batteries appeared (they are used today).

An externally serviced battery is a monoblock, in which there are several exits with covers at the edges (for topping up liquid).

How to Charge a Bosch S4 Battery

Despite all its advantages (large capacity, longevity, resistance to deep discharges), the battery required constant attention.

The course of electrochemical reactions led to the "burning" of the electrolyte and the need to top up with distilled water.

In particular, the main problem of the served power sources is the presence of antimony on the down conductor.

The latter through chemical reactions moves to the cathode and helps to reduce the voltage at the output of the battery.

The result is molecular decomposition, and then the active evolution of oxygen and hydrogen. The release of gases is so active that there is a process of "boiling".

In addition, during operation, the electrolyte invariably finds its way out (covers cannot be airtight forever). The composition that appears on the surface must be neutralized with an alkaline solution (for example, a mixture of water with soda).

How to charge serviceable batteries read HERE.

2. Maintenance free batteries.

A modern version of power sources. There are three types.

  1. With ordinary electrolytes inside, whose case is sealed on all sides. There is no possibility of adding distilled water.
  2. With liquid electrolyte that impregnates non-woven polypropylene.
  3. Gel batteries. Inside the hermetically sealed case is silicon oxide, which is impregnated with electrolyte. The whole mass is white.

A feature of gel batteries is the absence of an electrolyte inside, the role of which is taken by a special thixotropic gel.

The advantages of such batteries include:

  • the absence of problems with the gel, which does not overflow beyond the boundaries of the battery capacity and does not require topping up;
  • lack of self-discharge and the ability to survive a large number of charge and discharge cycles;
  • ease of use, because you do not need to think about the need to service the battery and perform any complex actions.

But, as a rule, maintenance-free batteries with ordinary electrolyte are used on cars, since they have an adequate price.

And gel batteries are used where long-term under load, power consumption is required. For example, on boat electric motors, electric cars, children’s cars, etc.

Problems in maintaining maintenance-free batteries

Despite the clear advantages, maintenance-free batteries have a number of disadvantages.

These can be attributed.

1. Checking the density and electrolyte level is not possible. For this reason, it is impossible to determine the real state of the power source and its efficiency.

You may know that the battery malfunctions and produces less voltage, but this cannot be fixed.

As for the guaranteed five-year service period (sometimes more), it often remains only in theory.

The battery will last its entire life only if it is used correctly (for example, with timely charging, proper storage in winter, and so on);

2. If there are leaks in the vehicle wiring, malfunctions in the vehicle’s generator, failure of the rectifier, or poor-quality belt tension on the generator, the maintenance-free battery will wear out faster. Subsequent troubleshooting will not change anything.

What are the disadvantages of the hydrometer?

To make life easier for motorists, manufacturers have provided a maintenance-free battery with a special charge sensor. the so-called hydrometer.

With increasing density (charging the battery), the indicator rises, and with a decrease (discharge) it drops.

But such a hydrometer has a number of disadvantages:

  • firstly, it often shows incorrect data, which misleads motorists;
  • secondly, the float is installed in only one bank, so you still have to keep the charging process under control;
  • thirdly, charging information can be obtained when reaching a capacity of 65%. With a subsequent charge (up to 100%), the position of the float does not change, so it will still not work to know the exact charge level;
  • fourthly, the indicator does not provide the necessary information if the electrolyte level has decreased before exposure of the plates.

Video: How to Charge a Bosch S4 Battery

What should I remember before charging?

Before you start the most important thing and start charging the battery, evaluate the age of the battery.

If the power source is more than five years old, then “saving” it and trying to charge it is useless. Even if something comes out, the battery will not last long. The only way for the "old man" is disposal.

Be careful when choosing the charger with which you will perform the work.

The best option is automatic memory, when a special program takes charge of the charging process.

Special firmware will independently give commands to change the charge current and voltage level. In addition, it is important to correctly connect the battery to the terminals of the charger.

In particular, the red terminal should be fixed on the “plus”, and the black. on the “minus”.

If the terminal does not have a color symbol, then orient yourself on the sockets of the charger (the corresponding symbols are marked on them).

An automatic charger is an expensive pleasure, so if charging is rare, it is better to seek help from a service station or take the device from a friend (friend).

And one more important point. In the process of charging a maintenance-free battery, harmful substances are released, so work in a well-ventilated room.

Battery Charging Instructions

The process of charging a maintenance-free battery is performed according to the following algorithm:

  1. Connect the wires with the correct polarity (as mentioned above).
  2. Set the required charge current. It should be 10% of the total battery capacity. For example, if the capacity is 70 amperes / hour, then the current level should not be more than 7 amperes. In the case when the battery is discharged to "zero", start charging from a lower current. 1-2 Amps.
  3. When connecting the wires to the battery, make sure that the charger is disconnected from the network.
  4. Once everything is connected and checked, you can turn on the charger and set the voltage level to 14.5 Volts. If there is a regulator, then set the current to the minimum level. This is enough to start charging the battery.
  5. During battery charging, the current level will gradually decrease. As soon as the voltage on the battery reaches 14.4 Volts, the current reaches the self-discharge parameter. 200 mA. In this case, remember that for serviced batteries, the basis is the rated charging current (10% of capacity), and for maintenance-free batteries, the voltage.
  6. If the power source was discharged to "zero", then the charge voltage should be reduced to the level of 12-13 volts. At the same time, control the charge current, which should not be more than 5% of the capacity of the power source. If this value is greater, then the voltage should be reduced.

It is important to read: Why the car’s battery is not charging, reasons, solutions.

Important information

Charging an unattended battery with a conventional charger is not recommended, although it is possible.

For these purposes, it is desirable to use automatic memory. Why is that?

So much easier and safer. The AZU itself will set the necessary charge parameters.

This will greatly facilitate not only charging a maintenance-free battery, but also increase the degree of its charge.

Let’s look at an example.

Take the Bosch S4 026 70Ah 0092S40260 battery, with a capacity of 72 A.h., with an operating voltage of 12V and an inrush current of 680 A.

The device has reverse polarity and European type of terminals.

If you set the charging voltage to 14.5V, then the Bosch S4 026 will charge about 80% per day.

If there is 15V at the terminals of the memory, then during this time, our copy will be charged approximately 90%.

If. 16. 16.4V, then in a day the battery will have a charge on 97%.

over, in all cases, the current value should not exceed 7.2, 1/10 of the capacitance.

It follows from the above that when using modern chargers, where it is possible to set the maximum charging voltage to not more than 14.5V, a maintenance-free battery will charge up to 97% of its charge for more than a day.

This is provided that the battery is partially discharged. And in the case of a full discharge, the charging time of a maintenance-free battery can reach 72 hours.

Also pay attention to the fact that at the initial stage of charging, the current strength can reach 50A.

Therefore, it is recommended to use such chargers, in the circuit of which it is provided to limit the charging current to twenty-five amperes.

We determine the degree of battery charge

In the case of maintenance-free batteries, accurate measurements cannot be made.

As a rule, the degree of charge is determined by the voltage readings, which are measured after 8 hours of a calm (not working) state of the battery.

At a temperature of at least 20 and no more than 25 degrees, the voltage at the terminals should be 12.7. 12.9V.

See table below.

Is it possible to measure the density in a maintenance-free battery

Theoretically, much can be done, but in practice, unfortunately, no. The same goes for maintenance free batteries.

Their device is very similar to ordinary batteries, except that their plugs are either hidden or sealed (we are talking about the battery in paragraph 1.).

Theoretically, you can pry and remove all this, and then measure the density, but in this case the tightness will disappear, which you can’t restore in any way.

Therefore, this method of measuring density in maintenance-free batteries is contraindicated and this is the main disadvantage of these devices.

In this case, you will have to focus only on the hydrometer, if there is one or a voltage indicator.

Useful Tips

Try not to operate a maintenance-free battery in overcharge and undercharge modes. Overcharge is when the voltage in the car’s power supply network is greater than 14.4V. Undercharging is less than 13.9V.

At least once every two to three months, check the voltage at the battery terminals.

Remember that the ideal environment for any battery is cold. At 5 degrees in a year and a half, any charged and serviceable battery will lose only 20% of its full capacity. At such temperatures, self-discharge is minimal.

If conditions permit, it is advisable to put a maintenance-free fully charged battery on a constant charge. The charge current is typically 200mA.

There will be no harm, and the battery will always be 100% charged.

But despite the foregoing, many motorists operate a maintenance-free battery that is not fully charged. As a rule, it is 90%.

This is done in order to protect the vehicle’s on-board network from power surges that may occur when the relay of the regulator or other devices fails.

In this case, the battery plays the role of a capacitor and absorbs an excess of voltage in the network, thereby saving the car’s electronics. In this case, the battery itself remains unharmed.

Important elements of the car’s electrical network are the relay regulator and generator. If they are working, then you will never get more voltage in the on-board network. 15.1V.

By periodically checking the operation of these devices, you will significantly extend the life of any battery, including a maintenance-free one.


Maintenance-free batteries are a double-edged stick. On the one hand, there are no operational problems. What is called. put, used and threw away.

On the other hand, with improper operation and errors during charging (its absence), the resource of the power source may decrease.

However, it will be impossible to do anything. There are cases when, after 1-2 years of service, once new batteries were sent to the trash.

So the task of a good car enthusiast is to know how to care for a maintenance-free battery and charge it in a timely manner.