How long does a completely dead car battery take to charge?
In most cases, a completely dead 12-volt lead-acid car battery will take several hours to reach a full charge. If you rely on the car’s alternator by driving, you may regain enough power to restart the engine after 30 minutes to a couple of hours, but a full recharge typically requires several hours or more with a proper charger.
Charging time depends on battery capacity (measured in amp-hours), the charging method and current, battery health, and ambient temperature. This article breaks down what “completely dead” means, how charging times are estimated, and what to expect under different scenarios.
What counts as completely dead and how is charging time measured?
A battery is often labeled “completely dead” when it cannot deliver enough current to crank the engine. Resting voltage can be a useful guide: a fully charged 12-volt battery typically reads about 12.6–12.8 volts; a voltage below roughly 12.0 volts indicates a discharged state, and substantially lower numbers can indicate a deep discharge or sulfation. Charging time is usually estimated by the battery’s capacity (Ah) and the charging current (amps). For example, a 60 Ah battery charged at 10 A would require around 6 hours of ideal charging to reach full capacity, plus extra time for inefficiencies and temperature effects. In practice, time can vary widely with battery age, condition, and charger quality.
Charging times by method
Below are common scenarios and the typical time ranges you can expect to move a completely dead battery toward a usable state. The ranges assume a standard 12-volt lead-acid or AGM battery and normal operating conditions.
: If you start the car with a jump or allow it to run and drive at highway speeds, the alternator can replenish a sizable portion of the battery over a few hours. Expect roughly 1–4 hours of driving to achieve a substantial recharge, and longer to reach a full 100% state of charge, especially if the battery is old or heavily sulfated.
: Very slow recharge suitable for maintenance or a deeply discharged battery left overnight. Time to full charge can range from 8–24 hours or more, depending on how deeply discharged the battery is and its age.
: A moderate rate that can bring a deeply discharged battery to a usable level in roughly 3–6 hours, with longer times if the battery is old or partially sulfated.
: Fast recharge possible in about 1–3 hours for a typical 40–70 Ah battery, but high currents generate heat and can stress older batteries. Always follow manufacturer guidelines.
: If sulfation is severe or the battery has reached end of life, charging may be ineffective. In such cases, replacement is often necessary even if a charger can deliver current.
These time ranges are estimates and assume typical battery health and temperature. Real-world results will vary based on the battery’s age, history, and the exact charging equipment used.
Practical scenarios and guidance
Scenario: Jump-start and drive to recharge
If you jump-start a vehicle and drive it for a period, the alternator will replenish a significant portion of the battery’s capacity. Many drivers report starting problems resolved after a 20–60 minute highway drive; however, a full recharge to peak capacity often requires several hours of continued driving or an additional charging session with a dedicated charger.
Scenario: Home charging with a portable charger
A dedicated charger at home is safer for long, slow charging. For a battery around 60 Ah, a 10 A charger can take roughly 5–7 hours to reach a full state of charge under ideal conditions; a 2 A charger might take 20+ hours. If the battery is older or deeply discharged, plan for additional time and monitor temperature to avoid overheating.
Safety and maintenance tips
Check the battery and charging system
Before relying on a charger or a jump-start, inspect the battery for obvious signs of damage, swelling, or leaks. Ensure terminal connections are clean and tight. If the alternator or charging system is faulty, recharging the battery won’t hold a charge and could leave you stranded.
When to replace rather than recharge
If a battery remains unable to hold a charge after multiple charging attempts, or if it frequently dies even after charging, it’s often more cost-effective and safer to replace it. Battery age is a major factor; most car batteries last 3–5 years under normal use, with performance deteriorating in extreme temperatures.
Summary
A completely dead car battery typically requires several hours to fully recharge, with shorter times to regain enough charge to start the engine. The exact duration depends on battery size (Ah), charging method and current, battery health, and temperature. Driving with the engine running or using a high-amp charger accelerates the process, while slow, low-amp charging can take many hours or more. If charging proves ineffective or the battery is old, replacement is often the best option.
How long would it take for a fully dead car battery to get full charge?
10-24 hours
Actual battery chargers take 10-24 hours to charge a car battery. That's the fast, smart chargers. If you're using a trickle charger, you could be charging your battery for three or more days.
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.
How long should it take to jump start a dead car battery?
Jumping a dead battery typically takes 10 to 15 minutes, but this includes a few minutes to connect the cables and get the booster car running, followed by time to start the dead car. After the car starts, it needs to run for at least 15 to 30 minutes to recharge, so plan for the total process to take between 25 and 45 minutes from start to finish.
Jump-starting process
- Connect the cables: Attach the red clamp to the positive terminal of the dead battery, then the red clamp to the positive terminal of the good battery. Connect the black clamp to the negative terminal of the good battery. Find a metal, unpainted part of the engine block to connect the last black clamp to (not the negative terminal of the dead battery).
- Start the booster car: Let the booster vehicle's engine run for a few minutes to begin charging the dead battery.
- Start the dead car: Attempt to start the car with the dead battery. If it doesn't start, wait a few more minutes and try again.
- Disconnect the cables: Once the dead car is running, remove the cables in the reverse order you connected them.
- Recharge the battery: To ensure the battery is fully charged, drive the car for at least 15-30 minutes. It's a good idea to turn off unnecessary accessories like the radio or air conditioning during this time to direct more power to the battery.
Factors that can affect jump-start time
- Battery condition: A severely dead battery may take longer to charge, potentially requiring more time to run the booster car and the "jumped" car before it can be started.
- Cable quality: Using higher-gauge, heavy-duty cables can speed up the process.
- Vehicle type: Larger vehicles like trucks and SUVs may require more time to charge a dead battery than a compact car.
- Weather: Cold weather can slow down the process and make it take longer for the battery to charge.
You can watch this video to learn how to jump-start a car: 31sKPTV FOX 12 | Local news, weather Portland, OregonYouTube · Oct 9, 2024
Can a completely dead battery be recharged?
A completely dead car battery can sometimes be recharged, but success depends on the cause of the discharge. If the battery is simply discharged but otherwise undamaged, a smart charger can be used to recharge it, although a conventional charger may not fully restore its capacity. However, if the battery is old, internally damaged, or has suffered extreme sulfation, it may not be rechargeable and will need to be replaced.
This video demonstrates how to charge a dead car battery using two methods: 57sInspiring BuildsYouTube · Aug 17, 2024
When a dead battery can be recharged
- Discharged but undamaged: If the battery simply went dead, a dedicated smart or multi-stage charger is the best option to fully and safely charge it.
- Sulfation is minor: Some specialized chargers are designed to help reverse the process of sulfation, which can be a cause of a dead battery.
When a dead battery likely cannot be recharged
- Internal damage: If the battery has internal damage from extreme temperatures or has a shorted cell, it is not rechargeable and must be replaced.
- Cracked or leaking: Do not attempt to charge a battery that is cracked or leaking, as this is a safety hazard.
- Old and damaged: A battery that is already old or has been repeatedly discharged is less likely to hold a charge even if recharged.
How to attempt recharging
- Use a battery charger: A smart or multi-stage charger is recommended to properly charge a modern car battery.
- Jump-start: You can use jumper cables to jump-start the car from another vehicle. Once the car is running, let it drive for at least 15-30 minutes to allow the alternator to charge the battery.
- Take it to an auto parts store: Many auto parts stores offer free battery testing and charging services.
