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Will an Alternator Charge a Dead Battery?

If you have a dead battery, jumper cables can be a real lifesaver. And while boosting the battery to get your car running can get you on your way, you shouldn’t rely on running your car to recharge the battery. It places enormous strain on your battery and the alternator and can contribute to premature failure in either or both. 

When you jump-start the engine, you’ll often hear a loud whining noise from the alternator, albeit temporarily. That’s because it’s being forced to work at 100% for a long period of time where it’s only meant to produce that kind of effort in short stints. It generates a lot of heat both at the alternator and at the battery. 

This amount of stress can cause the voltage regulator or rectifier diodes to fail, diminishing the charging output from the alternator. In the battery, sulfation can occur that essentially short-circuits plates inside after some time, leading to premature failure. 

If you have a dead battery, it’s always best to recharge it slowly with a plug-in battery charger.

Helpful Resources

Advice, how-to guides, and car care information featured on AutoZone.com and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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