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How Do I Know If My Car Battery Is Bad?

Fernando the electronics guy is an electronics engineer. He earned his Bachelor of Science in Electrical Engineering from UC Riverside.

Symptoms and Identification of a bad battery, alternator, or starter

Symptoms and Identification of a bad battery, alternator, or starter

Let's say your car is acting up. It's not turning over. What now?

If your car won't start, it doesn't necessarily mean your battery is bad. There are three possible causes:

  • the battery
  • the alternator
  • the starter.

Which is the culprit?

Signs of a Bad Car Battery

If your car battery is in its early stages of failing, you’ll notice dimmer lights:

  • Headlights
  • Exterior lights
  • Interior lights

You’ll also notice a weakened operation of other electrical components:

  • Power windows
  • Power steering
  • Windshield wipers
  • Defroster
  • Stereo
  • Display cluster

A bad battery may also cause other specific problems:

  • When you turn the key, there is a clicking noise under the hood, or the engine cranks slowly.
  • The car starts only when pressing the gas pedal.
  • The engine stalls because fuel injectors aren't getting the electricity they need.
  • The throttle is unresponsive because electrical actuation is not working right.
  • The airbag and engine oil lights go on due to incorrect voltage.
  • The battery may leak battery acid. You’ll see this commonly at the terminals of the battery. The leak may cause a smell of sulfur—rotten eggs, if you will.

What the Alternator Does

Since the alternator generates and regulates the electrical current charging your car battery, it is crucial to have a working alternator.

The alternator also has built-in rectifier diode(s) to both convert alternating current (AC) to direct current (DC) and regulate the direction of the generated current. It keeps the battery from discharging, only allowing charging of the battery.

Note that if your battery is bad, that could be a sign that your alternator is bad as well, because a bad alternator can cause the battery to deteriorate over time.

Possible Signs of a Bad Alternator

  • A bad battery (see above)
  • No starting, or trouble starting
  • Dimming lights with changing brightness
  • Battery not charging while the car is running
  • Battery discharging overnight
  • A squealing sound coming from under the hood (usually the alternator bearing). The sound may get louder when the heater or sound system is on.
  • A whining, "fuzzy" noise on your AM radio (set to lowest range). The sound is electromagnetic noise caused by a failing alternator.

What the Starter Does

The starter, a small motor powered by the battery, is attached to your engine and transmission. It allows your engine to turn, thus transmitting power to your transmission.

The symptoms of a bad starter are common and often leave consumers confused about what needs to be fixed, leading to expensive repairs elsewhere.

Symptoms of a Bad Starter

  • When you try to start, there is no sound, a whirring sound, grinding sound, or another weird sound.
  • The dashboard lights up but the car won’t start. No dimming.
  • The engine won't turn over even after jumpstarting, or even when the battery is fully charged (minimum 12 V)
  • Blown starter fuse.
  • Failed starter relay.
  • Smoke coming from these areas after turning the key to turn on the car—perhaps a short.

Where to Begin Figuring Out What's Wrong

So—bad battery, bad alternator, or bad starter? It’s easier to check the battery health first.

It’s also a lot easier to stop by your local auto retailer for a quick starting system test. They’ll hook up their electronic apparatus to your battery and test the whole system. They’ll let you know what is failing and what isn’t.

Other FAQ

You asked, I answer. Here are some of the most common questions I've received.

How to Know When Your Car Battery Needs Replacement

If you have a bad battery, this won’t damage the alternator or the starter, but it may damage other parts of the vehicle. If you have a bad alternator, it may damage the battery. If you have a bad starter, the engine won’t crank but the failure won't damage any other components.

It is recommended to change a battery when it is due for it. You can't keep jump-starting it forever.

How to Start a Car With a Dead Battery

The most common way to start a car with a dead battery is to jumpstart it:

  1. Find another car to help you jumpstart your bad battery. Position both cars close enough to connect batteries via jumper cables, but don’t let the vehicles touch each other.
  2. Turn off both vehicles.
  3. Using a jumper cable, clamp the positive terminal on one battery to the positive terminal on the other.
  4. On the good battery, clamp a jumper cable to the negative terminal.
  5. On the bad battery’s host car, clamp the other end of that negative cable to any ground on the vehicle. Be careful not to touch positive and negative clamps together.
  6. Turn on the good car.
  7. Crank the bad car.
  8. If this doesn’t work, wait 15-20 minutes with all cables exactly the way you attached them. This will slowly charge up the bad battery enough to try again.
  9. Try again.
  10. If this still doesn’t work, consult a technician.

How to Start a Car With a Dead Battery Without Another Car

Remove the dead battery and take it to an automotive retailer. They will charge it for you while also allowing their electronic battery charging systems the opportunity to give you feedback on whether or not your car battery is bad.

Another option: Pop out your powerful portable jump starter. Jump your vehicle with it and get going with no damage to your battery.

What's Your Jump Starting Recommendation?

If your battery is flat it is highly convenient and recommended to carry a powerful portable jump starter. Electronics guy recommends the NOCO lithium jump starter above.

These portable battery booster packs hold a charge that can bring your car battery back to life. Their end clips—called terminator clips—are the same ones found on conventional jumper cables.

Old jump packs used to be composed of lead-acid batteries. But the ones above that I recommend are lithium-ion battery powered. More current, better technology, more dependability.

Why choose lithium-ion jump starters:

  • 4X more power per volume
  • 6X more power per weight
  • Slower discharge rate (only 3-5% / month)
  • Long cycle life
  • Low maintenance, lasts longer
  • Power and capacity advantages
  • Cheaper
  • Good against cold weather (CCA, or Cold Cranking Amps, in cars)

This is all about dependability. The jump starter that I recommend above will keep you moving.

Further Reading

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

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