Alternators and car batteries work together to start your engine and power your vehicle's accessories. The key difference is that the battery is what powers your vehicle when the engine is not running, whereas the alternator charges the battery and powers the vehicle while it's running. Because these systems have similar functions, understanding how they work will help you know which component isn't working properly if you're having issues.

The good news is that it's not difficult to differentiate the symptoms of battery and alternator issues. 4 Wheel Parts is here to help.

How Alternators & Batteries Work

Alternators and car batteries work together to power your vehicle. However, they perform different functions, and understanding how they work is important if you need to replace the battery or alternator.

The battery is responsible to send power to the starter to turn the engine over. Batteries in cars also power your vehicle's accessories when the engine isn't running.

Alternators charge the battery when the engine is running and power accessories like the headlights, radio, and interior functions like electric seats, plus it delivers currents to the critical systems like spark plugs to maintain combustion.

Signs of a Broken Alternator

A broken alternator isn't too hard to spot when you know what to look for. The initial symptoms include things like a loss of power to interior accessories while driving. That said, problems may progress into something more serious.

Fluctuations in Power

One of the most obvious signs of a broken alternator is a fluctuation in power. When headlights are too bright or too dim, it's a sign that your alternator is going bad. You may notice inconsistent electrical functions in the cabin. For example, lights on the dashboard might be dim and other accessories may malfunction.

Noises or Smells Coming from Under the Hood

Noise and foul odors coming from under the hood are never good signs. Keep an eye on odors that smell like burning rubber or burning wires. Also, listen for whining noises or growling noises. The sound of clinking metal may also be an indication that the alternator is going bad.

Frequent Stalling or Dead Batteries

Stalling and dead batteries are also a sign of a bad alternator. The alternator charges the battery and supplies power to the computerized systems and spark plugs, so you may notice a clicking sound when you turn the key if the battery is dead. On the other hand, the engine may stall while you're driving if there isn't enough alternator output to keep the battery charged.

Signs of a Bad Battery

Several signs indicate a bad car battery. In fact, some of the symptoms are visible when you open the hood. Car batteries last for three to five years on average, so make sure you check your battery often.

The Car Doesn't Start

When a battery is bad, your vehicle often won't start. The battery is responsible for sending power to the starter, so without a functional battery the vehicle won't work. If the vehicle starts with jumper cables and the battery holds a charge for a few more quick starts, it's likely the battery and not the alternator.

Electrical Problems When the Engine is Off

One of the most obvious problems you'll notice is that your vehicle's lights and accessories won't work well when the engine isn't running. Some examples include the radio not working or the dashboard being dim. Also, you may notice that your HVAC system may fail if the battery is dead.

Corrosion

Corrosion is one of the quickest ways to determine if a battery is dead. When you pop the hood check the terminals for corrosion. It looks like powdery buildup around wires and terminals. Corrosion may also appear around other components and may result in blown fuses. While you can clean the battery terminals to remove battery acid deposits, it's best to test the battery and replace it if it fails.

Fixing a Bad Alternator

Alternators will display specific symptoms when there's an issue and to fix an alternator you'll have to replace it. The steps to replace an alternator are similar across most vehicles and it's possible to do it in your driveway.

1. Disconnect the Battery and Wires

First, disconnect the battery to prevent injuries or shocks. Then, remove any wires attached to the alternator. Depending on the vehicle, the number of wires will vary. Always wait a few minutes after disconnecting the battery before getting started. To disconnect the battery, start with the negative terminal to avoid injury.

2. Disconnect the Tensioner Pulley and Bolts

Alternators have a few things holding them in place. There's a tensioner pulley and a few bolts. The number of bolts depends on the vehicle but it's usually between two and four. Removing the pulley is the hardest part and may require a few tools to reduce the tension of the belt by turning a bolt or rod. Older vehicles may just have spring-loaded pulleys that you push back with a wrench.

3. Replace the Alternator

The next step is to replace the alternator. Remove the old alternator and examine the new alternator. Make sure the new alternator is the right fit for your vehicle and install it where the old one was. Once the new alternator is in place, connect the tensioner pulley and any bolts you removed from the old alternator.

4. Connect the Battery and Wires

Once the alternator is secured, connect the wires from the alternator to the battery. Make sure you start with the positive terminal and then the negative terminal when you connect the battery.

5. Test the Alternator

Before you close the hood and put your tools away, make sure you test the alternator. Start the engine and let the vehicle run. Check the voltage on the battery when the engine is running to ensure that it's charging.

Fixing Battery Issues

Battery issues will vary and may cause slight problems or prevent your vehicle from starting. Knowing what's wrong with the battery will give you a good starting place for when it's time to fix it. There are a few quick steps to help you fix any battery problem you're having and it's always best to replace a bad battery.

1. Disconnect the Battery

To disconnect a battery properly, remove the negative terminal first and then remove the positive terminal.

2. Clean the Area

Some bad batteries will have corrosion around wires, terminals, and in the battery holder. Before you install a new car battery, make sure you clean the area with a solution of water and baking soda. Having a wire brush will also help.

3. Connect the New Battery

Installing the new battery is a breeze. Place the new battery in the battery holder and connect the positive terminal first. Then, connect the negative terminal. From there, start the engine and check the voltage to see if everything is working properly.