Bad Alternator Vs. Bad Battery: What’s The Difference?

signs of a bad car battery vs alternator-unitechmotor


Ever questioned why your car behaves strangely? It usually comes down to either a loose alternator or a weak battery. They have different problems, but they are similar to the power couple in your car. A defective alternator and a bad battery give off other signals when they are not functioning correctly.

This quick read explains the straightforward indicators that can assist you in determining whether the alternator or the battery is making more noise.

So, fasten your seatbelts and join us. We’ll review the fundamentals of these automotive issues and how to identify them before they catch you off guard.

Difference between A battery and an alternator:

Following are the differences between a battery and an alternator:

Alternator Battery
It is a device that converts mechanical energy into electrical energy. The battery both stores and provides electrical energy to the various pieces of equipment.
The power to the alternator is provided through the crankshaft. The power is provided to the battery through an alternator.
The alternator is an alternating current AC device. A battery is a direct current DC device.
The battery may not charge properly due to a malfunctioning alternator. Problems starting a car can be attributed to a dead battery.
The specificity of the alternator is its current and voltage. The specificity of the battery is its voltage and capacity (Ah).
The alternator has motile components. The battery doesn’t have any motile components.
The alternator has the following components: stator, rotor, armature, pulley, etc. The battery has the following components: cathode, anode, electrolyte solution, etc.


Signs of a bad battery:

If you notice these signs in your battery, then your battery needs to be changed:

  1. Dashboard lights: Dashboard lights, such as the check engine light, can indicate that the alternator is not providing enough charge. This might indicate that your battery needs to be replaced.
  2. Uncommon Odor: An odd smell, often compared to rotten eggs, can indicate that the battery leaks gas. This smell will get stronger as the battery ages. If you notice this smell, you should contact your battery to be checked and replaced.
  3. Malfunctioning Components: If parts of your car stop functioning correctly, such as windshield wipers, headlights, air conditioning, or phone chargers, it could mean that your battery is weak. This can be a safety issue, so you should check your battery immediately.
  4. Slow Crank: If your engine cranks slowly or the lights flicker or make unusual noises when you try to start your car, it could mean your battery is weak. Pay attention to these warning signs.

If you can only start your car by pushing on the gas pedal, it could mean that your battery is weak. You should consider getting a new battery if this happens frequently.

  1. Backfiring: A backfire can be caused by a weak or defective battery that sparks intermittently. This can be especially dangerous if fuel builds up in the cylinders and is ignited, causing a backfire.
  2. Visible Corrosion: If you see a white or blue granular substance on your battery, it could mean the battery is corroding. This substance results from a chemical reaction between the battery acid and the metal parts of the battery. A small amount of corrosion is average, but excessive corrosion can indicate battery leaks or malfunctions.

Signs of a bad alternator:

Here are the key symptoms of a bad alternator.

  • Dimming Lights: If your alternator is not working correctly, your headlights and interior lights might dim.

. • Warning Light Illumination: The car’s dashboard has a light that appears to be a battery. This light is known as the warning light. If this light comes on while driving, your alternator is having trouble and must be fixed.

  • Strange Noises: A problematic alternator can make nonpleasing noises, like scratching and rough sounds. Accordingly, alternator mechanical problems need to be fixed right away.
  • Electrical Failures: Electrical failures can happen when the alternator is malfunctioning. Radio, dashboard, and power issues may occur.
  • Dead Battery: Although it may not seem connected to the alternator if the alternator fails, the battery may lose power. If you experience dead batteries, the alternator could be the reason.

To learn more about why these symptoms occur, check out “5 Signs of Alternator Failure.”

What does a battery do?

The following are the functions of a car battery:

The car’s power storage:

A car battery, which is often shaped like a rectangular box, is the power bank for a car. It stores the energy required to start and keep the car’s engine running. While the battery’s exterior may appear to be a simple block with connectors, the interior has a durable and acid-resistant plastic shell that protects the complex inner workings. These inner workings include a chemical solution, typically sulfuric acid, and lead and lead dioxide plate layers. These plates react with the acid to generate energy.

Energy to Start The Engine:

A car battery uses stored power to start the engine. It creates a chemical reaction between acid and plate materials (lead and lead dioxide). This reaction releases electrons and generates electricity. A weak battery can be recharged using a car charger. Batteries have different power strengths, which are measured by CCA (cold-cranking amperes) rating. A higher CCA rating is better for colder climates where engines may struggle to start. This is because batteries with higher ratings have more plates and solutions. However, the ideal CCA for a vehicle depends on the environment where it will be used, not just a higher number.

Delivers Electricity to the Ignition System:

When you initiate your car’s ignition, the battery receives a signal to trigger a chemical reaction that generates a strong electrical current. This current is required to activate the starter and power up the engine. The battery’s role at this stage is to release a powerful, short-lived electrical charge. Subsequently, the coil produces the high voltage necessary to drive the starter, pass through the distributor, and reach the spark plugs to ignite the fuel within the engine’s combustion chambers.

The battery helps regulate voltage:

Power surges can harm a car’s electrical systems, including the computer and ignition system. Fortunately, a car’s battery helps protect against this by regulating the voltage and preventing sudden spikes. The battery works with other fuse elements and circuit protection devices to ensure that the electrical systems receive the right amount of power.

It’s important to have a backup battery for the alternator. This prevents voltage surges that can harm the car’s systems. The voltage surge could be dangerous if the alternator gets disconnected from the battery. But if the battery is there, the change in power is slower and safer for the car’s systems.

What is the purpose of an alternator?

What Is An Alternator And How Does It Work? The alternator in your car produces electricity by converting mechanical energy to electrical energy. The battery starts the engine, and the alternator keeps the electrical current flowing while it is in use. An alternator’s primary purposes are listed here:

  1. Electricity Generation: The primary function of the alternator is to change engine power into electricity for use. A wire coil spins in a magnetic field to create an alternating current.
  2. Battery Charging: The vehicle’s battery depends on the alternator. The running engine uses electricity to charge the battery.
  3. Power Supply to Electrical Components: The alternator powers the air conditioner and lights, among other automotive components.
  4. Voltage Regulation: Alternators consist of a voltage regulator that stabilizes the electrical system. This guarantees that these parts function when the engine is running. Furthermore, it prevents the battery from being overcharged. It charges the battery to run the essential components.

Troubleshooting methods:

To test the car’s charging system:

  1. Start the engine and let it idle.
  2. Press the parking brake, then engage the neutral gear in the transmission.
  3. Turn on all accessories, including high beams, AC, and wipers, to maximize the load on the system.
  4. Increase the engine speed to 1500 RPM, but be careful not to exceed the alternator voltage of 100V.
  5. Next, measure the voltage between the positive battery post and the B+ terminal connector using a voltmeter. In normal conditions, the voltage should be 0.2V or less. If the voltage is 0.3V or higher, it indicates that the battery is undercharging.
  6. Then, test the voltage between the negative terminal of the battery and the alternator. The voltage should be around 0.05V. If it’s 0.1V or more, it suggests that the battery is overcharging.

To test the car’s charging system, observe the voltage readings between the battery and the alternator under different loads and engine speeds. High or low voltage readings can indicate issues with the charging system, such as undercharging or overcharging.

How do we temporarily solve a problem?

This method is the most commonly used. Possessing a portable jump starter or jumper cables and a battery, preferably an extra one you keep for yourself is essential.

First, to jumpstart a car using a portable jump start, ensure the car is turned off. Next, locate the positive and negative clamps on the portable jump starter and the positive and negative terminals on the car’s battery. Ensure the jump starter is turned off before connecting the clamps to the battery. Once the clamps are connected, turn on the portable jump starter and start the vehicle.


Remember, the alternator and battery are crucial. They both work together to enable dependable vehicle operation. When examining the alternator vs battery, notice their differences. Regular maintenance and inspections extend the life of the alternator and battery and save you money on repairs.

Understanding the roles of the battery and alternator is essential for safe driving and proper car maintenance.