The battery icon on the dashboard is lit: what does it mean and what to do?

    When you turn the ignition key, several warning lights come on the car's dashboard. Among them is the battery symbol. If the battery icon on the dashboard lights up red, it indicates issues in the electrical system that could have far-reaching consequences. We explain how to perform a simple diagnosis and understand why the battery light is on, as well as what to do in this case. 

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How the battery light works 

    After the ignition is turned on, the car's self-diagnostic system is activated—key warning lights related to airbags, ABS, oil pressure, and so on light up on the dashboard for a few seconds. This includes the battery icon. When the engine starts, all the lights typically turn off. But if the battery icon on the dashboard remains lit even after starting the engine, there is a malfunction. 

    Before moving on to the possible causes, let's understand how the battery light works. In brief, it can be described as follows. After turning on the ignition, voltage is supplied through a fuse to the light on the dashboard and then to the alternator. Accordingly, the indicator lights up. The alternator, in turn, begins charging the battery after the engine starts, producing the same 13–14 volts of voltage, which causes the warning light to turn off. This indicates there are no malfunctions in the car's electrical system and everything is working as it should. 

Why is the battery icon on the dashboard lit up? 

    The following indicates problems: after starting the engine, the battery icon is lit up or even flashing. Most likely, the alternator is not recharging the battery, and the stored energy may deplete very quickly. If you continue driving, the car will stall after some time, and the engine may not be able to restart. Operating the car in this mode can lead to electronic component failures and degradation of the battery itself. 

    Moreover, a stalled engine while driving on a busy road can create a hazardous situation, so if the battery icon lights up while driving, you need to address the issue as carefully and seriously as possible. 

            So, if the battery warning light is on, what's the reason? 

        ·         The tension of the alternator belt has weakened, or it has broken. 

        ·         The bearings of the alternator shaft are very worn (in this case, the light on the dashboard blinks unevenly).

 

        ·         The brushes of the alternator are worn out (this fault mostly applies only to old cars).

 

        ·         There are problems with the terminal contact on the alternator (even though they are protected, they can oxidize over time, resulting in reduced conductivity). 

        ·         There is an open circuit or a short circuit in the alternator winding (in this case, the light will burn dimly, and it will go out when the engine speed increases). 

        ·         The voltage regulator relay, which maintains the correct battery charge by regulating the current coming from the alternator to the car's electrical system, has failed (in this case, the battery light glows dimly, blinks, or stays on continuously). 

        ·         The diode bridge MOS is faulty (it converts the alternating current generated by the alternator into direct current: in the case of a malfunction, the red battery icon may either stay on continuously or blink). {alertWarning}

    According to statistics, the diode bridge in the alternator is the most common failure. The second most common reason is brush wear. A very rare and usually not sudden problem is with the shaft bearings. To learn more about what an alternator is, the possible problems with it, and ways to check it, our tutorial article will help. 

    The "battery check" light on the panel also lights up in the case of complete or partial battery failure, low electrolyte levels, oxidation of terminals, or problems with the battery wiring. This means the alternator may be working fine, but the battery itself simply does not accept a charge. We have also written about all possible battery problems. 

    Sometimes the battery light on the panel lights up due to damaged wires or contacts, and the battery icon blinks due to problems with the same contacts of the alternator, including the "ground," as well as a defect in the battery's power wire. 

    In addition, there are cases when the battery charging light is on only at idle, and goes out at higher revs. In that case, the problem lies in the brush assembly, and such engine operation is insufficient for the normal operation of the alternator. In this case, it is worth contacting a service and checking both the brushes themselves and the live rings on the alternator rotor. Most likely, the brushes will need to be replaced, and the rings should be sanded and cleaned. 

 What to do if the battery icon on the dashboard lights up? 

    Of course, it’s best to stop and find out what’s going on. But if the problem occurs while driving and you don’t have the ability to diagnose and fix the issue right away, don’t panic. The battery has a so-called reserve capacity, measured in minutes and indicated on the case (though not always). This means the battery is designed for emergency situations—when powerful energy-consuming sources (such as window and seat heaters, heater, audio system, high beams, and so on) are turned off, it allows you to use the stored energy to get home or to the nearest service station, where they can determine the cause of the malfunction and eliminate it. On average, with a fully charged battery, a car can travel about 40 kilometers, but only with energy consumers disconnected as much as possible. 

    If you decide to conduct the diagnosis yourself, start by checking the alternator drive belt—one of the common reasons why the battery icon may light up on the dashboard.

    How do you do that? You need to turn off the engine, open the hood, and inspect the belt: it should be intact, without signs of wear and cracks, and dry, without any signs of oil, water, or other liquids. Then check the degree of tension by simply trying to twist the belt with your hand—on the long “arm” between the pulleys, it should be able to twist about 90 degrees. Or you can press the belt with your thumb: it should flex no more than 6–10 mm; the specific value depends on the car model. 

    Then check the voltage on the battery. The simplest way is using a multimeter. Our separate articles will help you understand how a multimeter works, find energy leaks, and check the state of the battery. 

    A properly charged battery, in case the engine was recently turned off, should show 12.5–13.0 V. A discharged or defective one will be less than 12 V. Such a low value is the first sign that the alternator is not working. 

    To check the alternator, you need to start the engine, wait for the RPM to drop below warm-up levels, and measure the current at the battery terminals. Normal readings are 13.8–14.5 V (lower indicates undercharging, higher indicates overcharging). As an additional check, you can slightly increase the RPM—if the readings remain unchanged, staying within the normal range, everything is fine and there is no overcharge.

    Next, try turning on power consumers (high beam headlights, rear window defroster, climate control system) and check the readings on the multimeter again. They may fluctuate, but should remain within the same range—13.8–14.5 V. In the case of a working voltage regulator and a charged battery, the voltage will tend towards the lower end of this range since it should prevent overcharging the battery. 

     If the readings remain within the normal range in all cases, but the battery check light is still on, it may indicate a fault in the indicator relay itself. Checking it is simple: if the fault indication does not disappear when the ignition is turned off, it means the relay remains closed—this should not be the case, and it needs to be replaced. 

    When the multimeter readings are below normal (less than 13.8 V and falling), it means the entire car’s electrical system is operating solely on the battery. In this case, turn off all energy consumers to conserve as much battery charge as possible, and continue to the nearest service station or call a tow truck. For other ways to check the alternator, read the relevant guide in the Handbook. 

     In the evening, a car operating solely on the battery will show dimmer headlights and instrument panel lighting. This is also a sign that diagnosis is needed, or you should immediately seek service. 

     If the alternator is in good condition, the problem most likely lies with the battery itself. What should be done in such cases? 

Check the battery’s lifespan. We’ve discussed this in detail in the Tutorial. 

    If the battery is relatively new, you can clean the terminals with fine sandpaper to remove oxidation and check the reliability of their connection to the power cables. 

When this does not help, charge the battery using a specialized device. 

A definitive way to resolve the issue is to replace the battery with a new one.

          So, very briefly

          ·         If the battery warning light on the dashboard is on, there are two most likely causes: a faulty alternator or a malfunctioning battery.

          ·         First, assess the condition of the alternator: you can visually inspect it, check the tension of the belt, and then measure the exact voltage. The latter can be done easily with a multimeter.

          ·         If the alternator is fine, the problem is most likely with the battery itself.

          ·         Check the voltage on the battery, and if necessary, charge it with a special device or replace it with a new one.

          ·         If the battery warning light still remains on after this, you should take the car to a service center for a more detailed inspection for potential malfunctions.{alertSuccess}

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