How long does a car battery take to charge when dead?

When a car battery is completely dead, it can take several hours to fully recharge it. The exact time it takes to charge a dead car battery depends on factors like the battery's capacity, the charging method used, and the condition of the battery.

Understanding Car Battery Charging

Car batteries are typically 12-volt lead-acid batteries that store electrical energy to power a vehicle's electrical systems and start the engine. When a car battery is dead, it means the battery has been drained of its charge and can no longer provide enough power to start the car.

To recharge a dead car battery, you have a few options:

• Using a battery charger or maintainer


• Jumping the battery with another vehicle


• Driving the car for an extended period

The most effective way to recharge a dead battery is with a dedicated battery charger or maintainer. These devices are designed to safely and efficiently restore the battery's charge over time.

How Long Does Charging Take?

The time it takes to charge a dead car battery can vary, but it's generally in the range of 4-24 hours, depending on the following factors:

• Battery capacity: Larger batteries with higher amp-hour (Ah) ratings will take longer to fully charge than smaller batteries.


• Charging method: Faster chargers can restore a battery in 4-8 hours, while slower trickle chargers may take 12-24 hours.li>
  
• Battery condition: Older or damaged batteries may take longer to charge or may not be able to hold a full charge.

It's important to follow the instructions provided with your battery charger and monitor the charging process to ensure the battery is charged safely and effectively.

Tips for Charging a Dead Car Battery

• Use the right charger: Match the charger's voltage and amperage output to the battery's specifications.


• Charge in a well-ventilated area: Lead-acid batteries can release hydrogen gas during charging, which is flammable.


• Avoid overcharging: Most chargers have automatic shut-off features, but it's still important to monitor the battery's charge level.


• Consider battery replacement: If the battery is very old or damaged, it may be more cost-effective to replace it rather than repeatedly recharging it.

By following these tips and understanding the factors that affect charging time, you can effectively recharge a dead car battery and get your vehicle back on the road.

How long should I leave a car running to charge a dead battery?

This will provide only a surface charge, which is insufficient. To achieve a deep charge that allows you to return after four hours and start the car, the engine needs to run for at least 30 minutes. If you plan to let the car sit overnight, it should run for at least an hour.

How long does it take to charge a completely dead car battery?

Charging a completely dead car battery takes anywhere from 2 to 24 hours or more, depending on the charger's amperage and the battery's size. A slower charge (around 2-4 amps) is better for the battery and can take 24 hours or more, while a faster charge (8-15 amps) can fully charge a dead battery in about 2-4 hours. 
This video explains how different charger amperages affect the time it takes to charge a car battery: 50sOPTIMA BatteriesYouTube · Oct 30, 2024
Factors affecting charging time

• Charger Amperage: This is the most significant factor. A higher amperage charger will charge faster, but too high of an amperage can damage the battery. 
  • Fast charge: Using an 8-15 amp charger can take 2-4 hours for a standard battery. 
  • Slow charge: Using a 2-4 amp charger can take 12-48 hours or more. 
• Battery Size: A larger battery (measured in amp-hours) will naturally take longer to charge than a smaller one, even with the same charger. 
• Battery Condition: A battery that is old or has been completely discharged for a long time may take longer to charge or may not hold a charge at all. 

Charging recommendations

• For a full charge: Use a smart charger set to a lower amp setting to ensure a full and healthy charge without damaging the battery. A full charge can take a day or even a few days. 
• For a quick start: If you need to start the car quickly, a higher-amperage charger can be used to get enough charge in a few hours. After starting, the car's alternator will continue to charge the battery, but driving for 30 minutes at highway speed is recommended to ensure it gets a decent charge. 

This video demonstrates how to start a car with a dead battery and the importance of driving after a jump start: 33sCatfish MotorsportsYouTube · Nov 23, 2023
What to do if the battery won't charge

• If the battery is very old, it may have internal damage and will not accept a charge, notes AutoZone.com. 
• If the battery still won't start the car after a full charge, it's time for a replacement. 

Can AutoZone charge a completely dead battery?

Yes, AutoZone can charge a completely dead battery for free, but it may take a while and is not guaranteed to work if the battery is damaged. If the battery is salvageable, they will test and charge it for you, or if it's beyond repair, they can help you find a replacement. It's a good idea to call ahead to your local store to confirm they have the equipment and capacity to slow-charge a dead battery. 
What to expect at AutoZone

• Free testing: An AutoZoner can test your battery for free, even while it's still in your car. 
• Charging: If the battery is simply discharged and not damaged, they can charge it. 
• Replacement: If the battery fails the test, they will help you find and install a new one. 
• Slow charging: For completely dead batteries, they may use a slow-charging process which can take several hours. 
• Call ahead: It is recommended to call your local AutoZone before bringing the battery in to ensure they have the necessary equipment for a slow-charge. 

Will a completely dead car battery charge?

Yes, a completely dead car battery can often be charged, but it may not hold a charge long-term and a smart charger might not work. To charge it, you can use a dedicated battery charger, which might take 24 hours for a full charge, or use a jump start from another vehicle to give it enough voltage to begin charging on its own. If the battery has been dead for a very long time, it may be permanently damaged and need replacing. 
Methods to charge a dead car battery
This video demonstrates how to charge a completely dead car battery using a dedicated charger: 1mCatfish MotorsportsYouTube · Nov 23, 2023

• Use a car battery charger: 
  • Connect the charger to the battery according to the manufacturer's instructions. 
  • For a smart charger to begin, the battery needs to have a certain minimum voltage. If it's too low, the charger may refuse to start. 
  • In this case, you can try an older, manual charger or use the "daisy-chain" method: connect jumper cables from a working battery to the dead battery, then connect the charger to the dead battery. This provides enough power for the smart charger to begin its work. 
  • A typical charge can take up to 24 hours to complete. 
• Jump start the car:
  • Use jumper cables to connect a working vehicle to your dead battery. 
  • Once both cars are connected, start the working car and let it run for a few minutes. 
  • Attempt to start your car. If it starts, immediately turn off all accessories and drive for at least 30 minutes to allow the alternator to charge the battery sufficiently. 
• Take it to a professional:
  • Auto parts stores often offer free battery testing and charging services. 
  • A mechanic can test the battery and your car's charging system to see if the battery is permanently damaged or if there's an issue with the alternator.