How long does a completely dead battery take to charge?

Charging time for a completely dead battery depends on battery type, capacity, charger power, and health. In practice, a modern smartphone or laptop with fast charging often reaches full in about 1–2 hours, while a typical 12V car battery usually requires several hours on a proper charger (often 6–12 hours). If the battery is old or damaged, the process can take longer or fail to complete. The exact duration varies with chemistry, age, temperature, and equipment.

What counts as “completely dead”

“Completely dead” generally means the battery has been discharged to a level where it cannot operate the device or deliver usable voltage, and in some cases the battery’s protection circuitry may prevent charging until voltage recovers to a safe threshold. Different chemistries behave differently: lithium‑ion and lithium‑polymer cells need a minimum voltage per cell to begin charging, while lead‑acid car batteries can be so discharged that the charger takes longer to bring cell voltages back into a safe range. If a battery shows no response or emits heat, odor, or bulging, stop and seek professional help.

Typical charging times by device type

Below are general estimates for common devices under typical conditions. Actual times depend on charger wattage, battery capacity, and battery health.

• Smartphones and small devices (lithium‑ion): 0–100% often takes about 1–2 hours with modern fast chargers (roughly 18–65W); with a standard 5–10W charger, expect around 2–3 hours or longer.


• Laptops (lithium‑ion): 0–100% typically 1–3 hours on a dedicated high‑wattage charger (60–120W), with larger or older batteries sometimes stretching to 3–4 hours or more.


• Car lead‑acid batteries: From fully discharged to full on a typical home charger (6–12A) usually 6–12 hours; higher‑current chargers (20–40A) can shorten this to roughly 3–6 hours, assuming the battery is healthy.

Times are approximate and can vary widely based on temperature, battery age, and whether the device supports higher‑power charging or has degraded cells.

Notes on differences by device and circumstance

Charging speed is influenced by the device’s charging protocol, the charger’s maximum output, and the battery’s condition. Heat slows charging and can trigger protective limits, while cold weather can significantly extend the time needed. A battery that is sulfated or near the end of its life may charge to only a fraction of its original capacity.

Factors that influence charging speed

Understanding what slows or speeds up charging helps set realistic expectations. The following factors commonly affect how long a full recharge takes:

• Charger power and quality: Higher wattage chargers can reduce time, but devices may cap charging speed based on safe limits.


• Battery health and capacity: Aging reduces usable capacity and may slow charging due to internal resistance.


• Temperature: Charging is slower in cold conditions and can be limited at high temperatures to prevent damage.


• Battery chemistry and BMS: Lithium‑ion, lithium‑polymer, and lead‑acid have distinct charging curves and safety features managed by the battery management system.


• Cables and connectors: Poor or long cables cause voltage drop and slower charging.


• Initial state of charge and voltage: If the battery is extremely low, some devices require a brief pre‑conditioning phase before rapid charging begins.

Practically, using the charger recommended by the manufacturer and charging in a moderate temperature range will yield the most predictable results.

Practical tips for getting back up and running

To minimize downtime and maximize safety, consider these steps before and during charging. The following list explains common approaches and precautions.

• Use the device’s official charger or an equivalent high‑quality charger that matches the device’s specifications.


• For a completely dead car battery, a jump‑start or booster pack can provide enough power to start the engine; after starting, drive for at least 20–30 minutes to begin recharging via the alternator. If the battery won’t hold a charge, have it tested or replaced.


• Avoid attempting to charge a visibly damaged battery or one that emits heat, fumes, or bulges; seek professional help.


• Keep charging area well‑ventilated and away from flammable materials; do not charge near open flames.


• If the battery temperature rises significantly during charging, stop and allow it to cool before resuming, or seek service if overheating persists.

Most batteries recover fully only if they are healthy and are charged with appropriate equipment. Repeated deep discharges or chronically high temperatures shorten lifespan and can prevent full recovery.

Summary

Charging a completely dead battery varies widely by type and conditions. Smartphones and laptops often reach full power in about 1–3 hours with appropriate fast charging, while car lead‑acid batteries typically require several hours on a suitable charger (often 6–12 hours) and may take longer if the battery is aging or damaged. Key factors include charger power, battery health, temperature, and the device’s charging protocol. When in doubt, use manufacturer guidance, monitor for heat, and consult a professional if a battery cannot properly take a charge.

Can a totally dead battery be recharged?

Yes, a dead battery can be charged, but success depends on the battery's condition; a smart or trickle charger is the best method for a full, safe charge. If the battery's voltage is too low, a charger may not work, and if it's deeply discharged for too long, it may be permanently damaged and unchargeable. 
Charging methods

• Use a smart charger: These are designed to charge batteries slowly and safely and can sometimes break up sulfation, a process that can prevent a battery from holding a charge. 
• Use a trickle charger/battery maintainer: This type of charger provides a low, consistent charge, ideal for deeply discharged batteries or for keeping a battery topped off during storage. 
• Use a jump starter or jumper cables: This can provide enough initial charge to get a deep-discharged battery to a voltage where a smart charger can then take over, say Reddit users. 

This video demonstrates how to use a jump starter to give a dead battery enough charge to be charged by a smart charger: 57sInspiring BuildsYouTube · Aug 17, 2024
Important considerations

• Check voltage first: Before attempting to charge, check the battery's terminal voltage. If it's below 8 volts, it likely won't accept a charge and may be permanently damaged. 
• Avoid overcharging: While most modern chargers have built-in safety features, it's good practice to periodically check the battery to ensure it isn't being overcharged, especially if using older or cheaper models. 
• Don't rely solely on driving: Driving a car with a dead battery to recharge it can strain the alternator and is not the most efficient method, especially for a deeply discharged battery. 
• Consider battery age: An older battery is less likely to recover from a deep discharge than a newer one. 
• Consult a professional: If you are unsure about the battery's condition or how to charge it, it's best to consult a professional. 

How long does it take for a completely dead car battery to jump start?

Be sure not to touch any metal surfaces while connecting or disconnecting jumper cables as they may cause sparks which could ignite fuel vapors in either engine bay. As long as you follow these steps precisely, it should only take around 10-15 minutes for your car to be up and running again.

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 does it normally take to charge a dead battery?

24-48 hours
The Basics of Battery Charging
It varies based on the battery's capacity and the charger's amp rating. Here's a quick breakdown: Standard Charging: Using a 12V battery charger with a 2 AMP setting, it typically takes 24-48 hours to fully charge a dead battery. This slow charge is optimal for maintaining battery health.