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A Guide to Differentiating Between a Battery Versus an Alternator Failure

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When a vehicle isn’t turning or staying on reliably, it can disrupt many plans and cause stress. Unfortunately, it’s not always easy to tell if the issue originates from the battery or the alternator that charges it. The following guide offers clues for determining the likely cause before taking the car to an auto mechanic.


Dim Dashboard or Headlights

Since the car’s electrical system relies on the battery when it’s not running, it’s a good test to see whether the battery is dead or just low. When turning the ignition partway to activate the electrical system, the battery is dead if no lights turn on. However, if the headlights or the dashboard lights are dim, the battery is weak. Likewise, if you try to start the car and there’s a clicking sound, the battery is bad but not dead.

Terminal Corrosion or Warped Battery
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Check the battery to see if there is a build-up of corrosion. There may also be a rotten egg smell from the sulfuric acid. If there’s none, also look to see if it’s been warped, which indicates irreparable damage.

Slow to Start or Won’t Start

If the battery is fine visually, try to jump-start the car. If it starts and holds a charge to drive to the destination but won’t start back up, it’s probably a battery problem. Be sure to drive it long enough for the alternator to do its job.


Stalls or Lack of Cranking

If the alternator isn’t functioning properly, the battery won’t be able to hold a charge. A vehicle won’t even start without the alternator. If jump-starting doesn’t work, the alternator is probably to blame.

Flickering Lights or Disrupted Electricity

If the car is on and the interior lights flicker, have an auto mechanic inspect the alternator. Rev the engine to see if the headlights get brighter. Also, if the lights dim gradually, the alternator is likely the cause of the weakened battery power. The same thing can happen with the rest of the electrical components. So, have the alternator checked if the stereo acts up or the power windows are slower to move up and down.


Whether you think you’ve diagnosed the cause or not, take the car to the auto mechanics at JL Tire & Auto Service in Chantilly, VA, to find the cause and solution. Their ASE®-certified technicians are dedicated to helping you get back on the road safely as soon as possible. Whether for a domestic or foreign car, they can provide services from repairs to upgrades. Visit them online for a complete list of services, or call (703) 327-4366 to schedule an appointment.

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