Does a Weak Battery Affect Car Performance? [Here’s the Truth!]


Vehicle owners have to deal with battery problems at some point. Something as simple as forgetting to turn your headlights off may drain your car’s battery and leave you stranded. But, does a generally weak battery affect your car’s performance?

A weak battery can affect your car’s performance in multiple ways. It can prevent your car from starting, cause electronic malfunction, transmission issues, power steering, central locking, and can even affect acceleration indirectly.

A car battery plays a key role when starting a car. But, there are a number of different ways in which a weak battery can affect your car. But, how exactly does it affect your car? Let’s find out!

What Problems Can a Weak Car Battery Cause?

A weak car battery can cause problems such as preventing the car from starting, malfunction of electrical systems and accessories, and power steering failure. Other low probability problems include potential damage to sensitive elements like the ECU (Engine Control Unit) and other electronic modules.

Since the main function of car batteries is to store energy and hold a charge capable of turning your vehicle’s starter motor, the main issues caused are related to powering the ignition system as you crank up the engine. Once the car is running, the alternator charges the battery.

Other vital issues caused by a weak battery include lights becoming dimmer than usual, misbehaving electrical components, and power steering issues.

A worn-out battery that needs to be constantly jump-started or that won’t hold a charge can indirectly damage electronic components. Low voltage is a silent enemy; as the voltage decreases, the amps increase and this can damage electric or electronic components.

There are a few relatively infrequent issues that can also be caused by a weak car battery. These include damaging the alternator’s internal parts or the voltage regulator because the alternator will have to work harder than usual to charge the battery and supply enough voltage to the vehicle’s components to keep them running.

The low voltage of weak car batteries can trigger false error codes that are stored in the electronic modules’ memory fault. These error codes can cause malfunctions to systems like the cruise control and the power windows, among others, and can also erase some settings that cause problems in other components.

All these problems require a visit to a professional mechanic to be solved.

Symptoms of a Weak Car Battery

Fortunately, you can tell whether the car battery is weak before it dies completely as long as you are aware of some of the common symptoms it exhibits!

I’ve listed some of the common symptoms of a weak car battery below –

1. Enginge Hard to Start

  • Hard to Start Engine: if you are having a hard time whenever you start your engine and you feel that the starter motor is spinning slowly or your engine doesn’t start as fast as usual, you probably have a weak car battery.
  • The Engine Won’t Start: if you hear that the starter motor is barely spinning and your car doesn’t start, your battery is probably dead.

    Sometimes your interior lights will turn on as you open the door as usual, and you may even be able to switch your dashboard lights and headlamps on, but your battery power won’t be enough to make the engine starter work.
  • Clicking Sounds: if you hear just clicking sounds when you switch the ignition key on, the problem is probably your battery. Your car battery doesn’t have enough charge to start turning the starter motor. Sometimes the click comes from the starter motor itself while others what you hear is a relay trying to make your starter motor work.

2. Electric and Electronic Devices Act Funny

Sometimes, you might notice that some or multiple electronic devices in your car function in a weird manner!

For example, the gauges on your instrument cluster may act funny as you switch the ignition on. Modern vehicles’ instrument clusters are electronic, and the gauges are powered by small motors driven by an electronic controller. A poor voltage input can make the gauges act weird and make noises as they move.

Power windows are other components that will usually give you a hint that your battery is weak. They won’t roll up or down as you press the switch on the door or the key fob, or they will do it very slowly as if they were set in slow motion.

Another device that may act funny is the radio. Depending on the head unit, you may see the LCD flashing waiting for the security pin code to be entered, or you may find out that all the settings of your stereo are gone, just to mention some of the possible problems that you may find.

Memory seats, electric side mirrors, wiper blades, and other components may also give you a hint that something is wrong with your battery.

3. Dim Lights

If you notice dimmer than usual interior or dome lights when you open the door, these are another symptom of a weak battery. Dim headlights when the engine is off are another indicator of a weak battery, while dim headlights when the engine is running may be a symptom of a bad alternator.

4. Key Fob Issues

A weak battery can affect your car’s alarm system. You may find problems to open your car using your key fob. If your car has a proximity access system, you won’t be able to use it either. You will have to find a way to manually open your car perhaps using a physical key.

5. Your Battery Gets Discharged Faster Than Usual

A fully charged battery working in a good condition should hold a charge even if you forget to turn off your headlights for a couple of hours or forget the interior light on for the night. Your car battery should usually survive a few weeks even if you haven’t used your car.

If your battery is completely dead much sooner than usual after one of these episodes, it’s probable that you will need a new battery soon.

6. Corroded or Sulfated Battery Terminals

If you notice that your battery terminals are corroded and/or sulfated, it’s a sign that your battery isn’t in its best shape. Cleaning the battery terminals may help you to extend your battery’s life.

However, if the car battery terminals remain corroded for a long time, it can mean that the battery is going to die soon.

Can a Weak Car Battery Cause the Car to Run Rough?

Generally speaking, a weak car battery won’t cause the car to run rough. If the battery doesn’t have enough power, it may not crank up the engine. However, once the car is started and the engine is running, chances of car running rough due to a weak battery are extremely low.

At the end of the day, it really boils down to your battery’s health. If the battery had enough power to crank up your engine, it’s unlikely that it may cause the car to run rough. Once your engine is running, the alternator will charge the battery and will keep your engine running smoothly.

On some rare occasions, and when the battery is damaged and unable to provide enough power due to one or more failing cells, the battery will act like a “sponge”, absorbing the alternator’s charge, and preventing the electricity from flowing through it. This will affect vital engine components like the ECU (Electronic Control Unit), the ignition system, and the electric fuel pump, causing the car to run rough.

Weak batteries put a good deal of stress on vehicles’ alternators; they have to work hard to charge the battery and supply the electric and electronic systems with enough power. Many modern vehicles use the ECU to control the alternator’s output voltage, keeping it below a safety threshold.

It is probable that these vehicles don’t run smoothly because the alternator isn’t able to build up enough power to charge the battery and keep the engine running.

Can a Low Car Battery Affect Acceleration?

Photo by Chandan Shastri on Unsplash (further edited)

A low car battery can affect acceleration indirectly. A poorly charged or defective battery can affect the proper functioning of elements of the engine management system, ignition components, and other parts that play a key role in car acceleration and keeping the engine running.

Engine components like the MAF, MAP, CKP, and other sensors use a reference tension that needs to be precise and steady. Besides, they need to be powered by at least 12.6V to function properly.

The same goes for the ECU, the engine’s computer, which needs good and steady power to do its job. The coils’ functioning may also be affected depending on their design and engine model. This may result in a hesitating engine and affect the vehicle’s acceleration.

The same goes for the fuel pump; if a fuel pump doesn’t receive enough power, it won’t spin fast enough to build sufficient fuel pressure, causing fuel starvation.

Can a Weak Car Battery Cause Transmission Problems?

Weak car batteries can cause problems in automatic transmissions if the tension levels get below a certain threshold. The Transmission Control Unit (TCM) in a modern transmission uses power from battery to switch valves on and off, and to power solenoids that control the transmission’s moving parts.

Most modern transmissions have their own electronic controller called the Transmission Control Unit (TCM) uses reference voltage and needs at least 12.5 volts to work properly. A weak car battery can make the TCM store ghost errors in its memory fault generated by the low voltage operation.

These errors can put the transmission in “emergency mode”, causing the transmission to shift slowly and disabling some functions like “sports mode” or preventing the paddle shifters from working.

Sometimes the transmission will stay in “emergency mode” even after the battery has been charged or replaced, and the errors will have to be erased with a scan tool to make it fully functional again.

Besides, most automatic transmissions have sensors that lock the shift lever in the park position. These sensors work with low-voltage signals that unlock the shift lever if certain safety conditions are met; for example, if the brake pedal is pressed.

If the voltage is too low, the shifter may stuck in this position, leaving the vehicle stranded. Most automatic transmissions have emergency procedures that enable users to unlock the shifter from “P” to tow the vehicle.

Some new models have modern automatic transmissions that don’t work with a lever but with buttons. These transmissions don’t have a mechanical connection to the gearbox; everything works electronically. These transmissions are hard to operate if the power is not enough to make their complex electronics work properly.

Can a Low Car Battery Affect the Air Conditioning?

It’s really hard for a low car battery to affect the air conditioning even though certain components of the air conditioning derive power from the car battery!

Let’s take a deeper look.

Car air conditioning systems rely on a compressor that is powered by the serpentine or accessories belt. When you turn on your AC, an electric signal is sent to engage the compressor’s clutch, which works as an electromagnet.

It’s almost impossible for the AC compressor’s clutch not to work because of a weak battery; however, there are other components of the air conditioning and heater systems, such as the evaporator fan and the blower that can be affected.

Besides, if you have a modern car with an “intelligent” HVAC system, there are more chances that you may experience AC problems. These systems have many electric parts which are commanded by an electronic module.

As we have seen before, low voltage can make electronic modules fail, that’s why these kinds of systems are more prone to fail than traditional systems with manual controls and knobs.

Can a Dead Car Battery Damage Your Car?

A dead car battery can damage your car. Low voltage can be harmful to electric and electronic components such as the ECU and the TCM, not to mention high voltage peaks that most dead car batteries are unable to absorb. This can cause serious damage to your car.

We have also seen that a weak battery will put a lot of stress on your car’s alternator, shortening its lifespan, and potentially damaging the alternator’s internal parts and/or the voltage regulator.

It’s important that you try to keep as few accessories on as possible to avoid overcharging your alternator and other electric and electronic components of your car as soon as you notice that your battery is weak.

Besides, a dead battery overheats the whole charging system, not to mention the hazards of jumpstarts. That’s why it’s important to try to replace your battery before it’s too late.

Can a Car Battery Affect Gas Mileage?

A car battery does not affect gas mileage unless the low voltage affects the ECU, altering the reference voltage of the MAF (Mass Air Flow) and the oxygen sensors, making the engine burn more fuel than usual.

If the battery is in good shape, the gas mileage will improve as the battery is charged by the alternator.

Does a Car Battery Affect Power Steering?

A car battery can affect power steering if the vehicle is fitted with an electronic power steering system. However, a battery will not have any affect on the power steering if the car is equipped with a hydraulic power steering.

Vehicles equipped with electric or electronic power steerings can have power steering problems in cases of bad, weak, or dead batteries. These systems use an electric motor to aid the driver to steer the vehicle lighter. A weak battery makes the car hard to steer as the electric motor won’t have enough power to work properly.

Some systems just won’t work when they don’t get enough power, leaving the driver without any assistance.

Does a Dead Car Battery Affect Central Locking?

A dead car battery will prevent the central locking from working. The key fob and/or the keyless entry will stop working due to the lack of electric power. The same will happen if you try to lock the doors. You will have to find a way to unlock and lock the doors manually.

Check your vehicle’s user manual to find out how to do it in your car.

Can a Car Battery Affect Brakes?

A car battery can’t affect the brakes directly, however, low voltage of the battery can affect the Anti-braking System (ABS) module and the ABS pump. If that happens, the ABS light will appear on the dashboard, and the ABS will shut down.

In certain cases, if the battery level is too low causing the ABS to shutdown, the engine won’t start at all.

Can a Bad Car Battery Cause Engine Misfire?

Technically speaking, a bad car battery can cause an engine to misfire, but it is extremely unlikely. Engine misfiring is usually caused by a worn-out spark plug or by an ignition coil that fails to cast a spark strong enough to burn the air-fuel mixture in time, causing a weak explosion and making the engine lose power.

There are a few ways in which a bad car battery can cause an engine to misfire. For example, if the alternator also fails as it’s charging the battery, the engine will shut off and in this case, it’s probable that the engine will misfire for a short time before shutting off.

Another way in which a bad car battery could cause an engine to misfire would be as a result of a failing ECU or sensor/s in charge of the fuel management system, or a coil or coil pack failure caused by the low voltage.

This can only happen when the battery is damaged. Otherwise, as the battery charges, the possibility of an engine misfire will decrease to zero.

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