Differences between a starter vs alternator vs battery

What are the key differences between a starter, alternator, and battery?

The starter, alternator, and battery are designed with different functionalities in mind. Yet, they all work together to start the engine and keep it running without cutting off prematurely (i. e. keep operating until the ignition is turned off).

The alternator is designed to convert mechanical energy (stored energy) into electrical energy (which causes an object to move). This electrical energy is used to charge the battery of your car while you are driving.

The starter works differently. This is because it takes the power of the battery to crank the engine.

The most significant role of the car battery?

Though the battery plays many roles, its most significant role is to start the engine. Therefore, the battery must store enough energy to power a car. If the power of the battery has been drained for any reason, the car will not start at all.

The most important role of the car starter?

The most significant role of a car starter is to enable the vehicle’s starter system to work properly. It has a motor that turns the engine over during ignition and it allows every other associated function to happen.

The most significant function of the car alternator?

While most people may think the battery is providing the main power source for their car, this is not really how the process works. Instead, it is the alternator that serves this purpose. The alternator plays the role of charging the battery while you are driving.

How do you know if it’s a bad starter, a bad alternator, or a bad battery?

Whenever a car does not start, the culprit may be either one of these 3 devices. Because all of these devices are designed to work together, even a minor malfunction in one of their components can keep the vehicle from starting.

With that being said, here are some common symptoms that are associated with each.

Symptoms of a bad starter

  • Engine Won’t Turn Over
  • Noise – Clicking, Grinding, or Whirring
  • Intermittent Issues Starting the Vehicle
  • Starter Stays On After Starting
  • Starter Engages But Motor Won’t Star
  • Battery
  • Smoke is coming from car – starter circuitry overheated

Symptoms of a bad alternator

  • Dim or Overly Bright Lights
  • Dead Battery
  • Slow or Malfunctioning Accessories
  • Trouble Starting or Frequent Stalling
  • Growling or Whining Noises
  • The smell of Burning Rubber or Wires
  • Battery Warning Light on Dash

Symptoms of a bad battery

  • A sudden, slower start
  • Headlights and power, but no start
  • No radio
  • Swollen battery size
  • An odd smell comes from the battery
  • Battery is old
  • Check engine lights flashing
  • Vehicle starts, then dies immediately – intermittent starting issues

As you can see, some of the same symptoms appear under more than one device. Therefore, whenever you or your mechanic is troubleshooting a startup problem, they may need to narrow down the scope of the search to get to the exact source of the issue.

For instance, if are having intermittent starting issues, it could be a bad battery or a bad starter. On the other hand, if you no longer have a radio, it is most likely a dead battery.

How much does it cost to replace a bad starter?

The price for a brand-new starter usually varies. Car owners can expect to pay around $50 – $350 for the starter, And a qualified mechanic may charge between $150 – $1,100 for labor. This means the cost of replacing a bad starter could be about $200 to $1450.

How much does it cost to replace a bad alternator?

The price for a brand new starter can also differ based on the cost of the part and the labor. Car owners can expect to pay around $100 – $350 for the alternator, And a qualified mechanic may charge between $350 – $400 for labor.

This means the total cost of replacing a bad starter could be about $450 to $750 if no other parts need to be repaired or installed (i.e. serpentine belt, may cost another $20 to $50)

How much does it cost to replace a bad battery?

The price for a brand-new battery will depend on some factors, including the size of the battery, the power, and the quality. Car owners can expect to pay around $45 – $250 for the battery.

A qualified mechanic may charge between $10 – $100 for labor. Or, if you buy your new battery from a car parts retailer, their onsite auto technicians may provide these services for free.

It is also important to note that the prices above can vary significantly based on several different factors. For instance, luxury vehicles may cost more based on the make, model, and year of the vehicle.


Though the battery, alternator, and starter are designed with different functionalities, they still work together to start your vehicle and keep it running smoothly.

Each of these devices plays a critical role in ensuring the engine gets the power that it needs when the ignition is turned on.

Also, once you learn the function of each, and how they work together to start your vehicle, it becomes easier to troubleshoot problems when they occur.

This is especially true if you know the symptoms to look for when one of these parts goes bad. You will know that a sudden, slower start is usually related to a bad battery.

You will also know that dim or overly bright lights are often associated with a bad alternator. In either case, as people learn more about the differences between the function of the battery, the alternator, and the starter, it is easier to identify potential problems and troubleshoot them, too.

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