Blink Fast! Why Your Car Battery Light Comes On and Off

  • May 22, 2023
Car battery light turning on and off Car battery light turning on and off

It's normal for your battery light to come on and go off when you first start your car. But if the battery light comes on and off while driving or stays lit as you drive, your battery or the charging system may be at fault. The battery light on your dash could indicate a minor issue like built-up corrosion on the battery's terminals or a more complex problem like a failing alternator. Keep reading to get a better idea of what may be causing your specific car battery light woes. 

How Your Car's Charging System Works

While your car's battery provides the electricity necessary to start the engine, the charging system keeps the engine and electrical components like lights running smoothly. If the charging system fails or provides insufficient electricity to the battery to keep it topped off, your car may eventually stop. So, if the battery loses charge faster than it's being recharged, you could be left stranded.

Your car's charging system consists of three main components: a battery, an alternator, and a voltage regulator. The alternator charges the battery by converting the engine's rotational power to electricity, typically via the serpentine belt. But, to ensure a safe charging voltage, the alternator's power must first go through the voltage regulator. If these critical elements fail or their connections are compromised, the charging system will not function properly. In effect, you will likely see an illuminated car battery light on the dashboard.

Why Is Your Car Battery Light Blinking On and Off

Some issues that can cause the battery light to flash intermittently may be easier to resolve than others. Let's examine the most common culprits behind a battery light flashing on and off before discussing why this light comes on at different driving intervals.

Corroded Battery Terminals

Corrosion buildup can impede electrical flow and conductivity, resulting in an undercharged battery and reduced voltage output for the vehicle's electrical devices. In extreme cases, the corrosion buildup may even prevent engine start-up.

Some battery corrosion is normal, especially if the battery is several years old. But if you notice excessive corrosion, there may be an issue with the battery or the alternator's voltage regulator — especially if the corrosion is concentrated at the positive terminal.

Commercial cleaners or a battery terminal cleaning tool can remove battery corrosion. However, be extra careful not to get corrosive materials on your skin or eyes. Corrosion is harmful to your health, and so are the gasses from lead-acid batteries. If you suspect your battery is leaking, take your vehicle to your nearest Tires Plus, and our technicians can safely clean or replace your battery if needed. 

Loose or Damaged Battery Cables

Cables connecting to your battery's terminals must be adequately tightened (not loose or too tight). In addition, damaged cables or clamps that wrap around the terminals can adversely affect the electrical flow to and from the battery. Ensure the cables are not broken and have a good connection with the clamps attached to the terminals. 

Bad Battery

Many signs may indicate your car battery is failing, like dim lights, slow crank, engine backfiring, and clicking sounds when you turn the key. But the most obvious sign is an illuminated car battery light on your dashboard. 

The average car battery life is 3 to 5 years, but driving habits and local environmental conditions can impact this estimate. For example, extreme hot and cold temperatures negatively affect lead-acid batteries. In addition, frequently taking short trips (less than 20 minutes) may not allow the alternator to sufficiently recharge the battery, potentially shortening battery life. 

A healthy car battery should output around 12.6V at its terminals when the car is not running. Use our free virtual battery tester for battery life prediction and assessment if you don't have a voltmeter. 

Replacing a failing car battery will resolve the light on your dashboard if this is the underlying issue. Fortunately, our car battery services include battery and charging system checks and battery replacement. We install a wide range of DieHard batteries — depending on your specific needs — with excellent warranties and long life cycles for maximum longevity.

Worn Serpentine Belt 

The alternator relies on the serpentine belt to spin its pulley and generate electricity for your car's battery and electrical system. However, if the serpentine belt is frayed, cracked, or thinned out, it can slip over the pulley and reduce the rotational force it provides to the alternator. But if the belt is completely broken or comes off the pulley, the alternator won't generate any power. 

Either of these scenarios can cause the battery light to appear on your dash. Sometimes the alternator belt will have traction but only slip occasionally, which could cause intermittent battery light flashing. Replacing the serpentine belt will likely resolve this issue.

Malfunctioning Alternator

Even if the serpentine belt spins the alternator pulley just fine, your battery power could be low if the alternator itself fails. As a result, you will likely see the battery light flashing on your dashboard. 

One of the most apparent signs of a failing alternator is when the output voltage drops on your car battery when you start the engine. The alternator's purpose is to charge your car's battery, and to do that, the alternator must output a slightly higher voltage than your car's battery. So, if the battery voltage drops below 12V instead of rising to about 14V once the engine is running, there is a high likelihood that something is wrong with the alternator. Common alternator issues are worn bearings and the decoupler pulley failure, but something could also be wrong with its rotor and stator.

You can test your car battery voltage output before and after the engine is running using a voltmeter, or bring your car to your local Tires Plus service center, and one of our technicians will do this for you. 

Faulty Voltage Regulator

Your alternator may contain one vital component — the voltage regulator. If this regulator fails, your car battery will receive excessive voltage, potentially causing it to get hot, amass excessive corrosion on the terminals, crack and leak, and ultimately die sooner. 

The voltage regulator ensures that the battery receives a safe voltage from the alternator because the alternator can produce a higher voltage than the battery requires.On older vehicles, the voltage regulator is a standalone unit as a part of the alternator, so, you can simply replace the voltage regulator and keep your alternator if it works fine. With newer vehicles, the voltage regulator is an internal part of the alternator, and the complete unit would need to be replaced.

Some modern vehicles don't have a voltage regulator. Instead, their engine control module manages the amount of voltage the alternator produces.

Why Your Battery Light Comes On When Accelerating

One telltale sign that something is wrong with the alternator's electrical output is when the battery light comes on when accelerating. When increasing speed, your engine works harder and requires more energy from your battery to keep running. If there is nothing wrong with the charging system, the battery gets a charging boost from the now faster spinning alternator. 

However, if the alternator is failing or the serpentine belt is slipping, the battery voltage will decrease when accelerating. This is thanks to the engine drawing more power and the charging system failing to keep up. As a result, you'll likely see the battery light turning on when accelerating. 

Why Your Battery Light Comes On At Idle

Several issues can cause your battery light to come on when your engine is at idle. But the first thing you should consider is your battery health. If you have an old car battery, it may not have sufficient voltage output for your car's electrical demand. So, if the car idles, the alternator output may not be enough to meet the electrical demand if your battery is failing. So, when you throttle up, the alternator provides more energy, causing the light to turn off.

Other causes include a bad voltage regulator, slipping belt, or alternator issues. If you are positive that your battery is in good condition, figuring out why the battery light is on only at low engine RPMs will require a thorough examination by experienced Tires Plus technicians. 

Get Your Entire Charging System Checked at Tires Plus

While we listed some common reasons behind the dreadful battery light on your dash, your car may experience multiple issues simultaneously, like a failing battery, a bad alternator, and a slipping belt. It can sometimes be challenging to pinpoint the problem. So, remove any doubts and visit your neighborhood Tires Plus for a full vehicle inspection and peace of mind.

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