How Long Does It Take to Fully Charge a Car Battery?

For a typical 12‑volt car battery, a smart charger takes about 4–8 hours at 10 A, 8–12 hours at 6 A, and 24–48 hours or more on a 1–2 A trickle/maintainer; an alternator can recover a partial discharge with 30–120 minutes of driving but won’t fully “top off” a dead battery quickly. If you meant an electric vehicle’s traction battery, Level 2 home charging generally takes 6–12 hours, while DC fast charging brings 10–80% in roughly 20–40 minutes but slows significantly from 80–100%.

“Car battery” can mean the 12‑volt lead‑acid starter battery found in gasoline and hybrid cars or the high‑voltage traction battery in an EV. Charging time depends on battery size, starting state of charge, the charger’s power, temperature, and how the charging system tapers current to protect the battery as it fills. The sections below break down realistic timelines and how to estimate your own.

What Do You Mean by “Car Battery”?

There are two very different battery types in modern cars. The 12‑volt starter/auxiliary battery (usually lead‑acid, sometimes AGM or lithium) powers starting and accessories—and is charged by a smart charger or the alternator. Electric vehicles also have a high‑voltage traction battery (measured in kWh) that is charged via Level 1, Level 2, or DC fast charging. Times and methods differ widely, so pick the section that matches your situation.

12‑Volt Starter Battery: How Long Charging Really Takes

Typical times by charger size

Charging time for a 12‑volt battery is mainly a function of how many amp‑hours you need to replace and the charger’s current. The values below assume a healthy ~50–70 Ah battery at room temperature and a modern smart charger that tapers current near full.

• 1–2 A maintainer/trickle: 24–72 hours to fully recharge a low battery; ideal for slow restoration and storage maintenance.
• 4 A smart charger: roughly 12–18 hours from low; faster than a maintainer but still gentle.
• 6 A smart charger: about 8–12 hours for a typical 50–70 Ah unit at moderate discharge.
• 10 A smart charger: roughly 4–8 hours; a common “overnight” solution.
• 20 A shop charger: about 2–4 hours, but verify your battery can accept this rate; smaller batteries can be stressed at high current.
• Alternator (driving): 30–120 minutes can restore a moderate deficit (e.g., after lights were left on briefly), but alternators are not ideal for deep recharge or full saturation; idling takes longer.

Expect slower charging in cold weather, with older/sulfated batteries, or when the charger tapers aggressively as the battery nears full. Deeply discharged batteries often need extra time in the absorption phase to reach 100% charge.

Quick formula and examples

You can estimate time with a simple rule of thumb: time ≈ (amp‑hours needed ÷ charger amps) × 1.2–1.4 to account for charging inefficiency and the absorption phase. Here are practical examples.

1. 50 Ah battery at 50% (needs ~25 Ah): at 10 A → (25 ÷ 10) × 1.2 ≈ 3.0 hours; real‑world 3–5 hours.
2. 60 Ah battery at 30% (needs ~42 Ah): at 6 A → (42 ÷ 6) × 1.3 ≈ 9.1 hours; real‑world 9–12 hours.
3. 70 Ah battery nearly empty (needs ~60 Ah): at 2 A → (60 ÷ 2) × 1.3 ≈ 39 hours; plan for ~40–48+ hours.

This method gives a realistic window; final “top‑off” often takes longer than the bulk phase because smart chargers reduce current to protect the battery.

Factors that change the timing

Several variables can shorten or stretch charging time beyond the rough figures above.

• Starting state of charge: Lower SOC means more amp‑hours to replace.
• Battery capacity (Ah): Larger batteries take longer at the same charging current.
• Temperature: Cold slows chemistry and can reduce charge acceptance; avoid charging a frozen battery.
• Age and health: Sulfation or internal resistance in older batteries increases time and may prevent full charge.
• Chemistry: AGM/EFB often accept slightly higher currents than flooded lead‑acid; 12‑V lithium (LiFePO4) needs a lithium‑compatible profile and should not be charged below 0°C.
• Charger behavior: Smart chargers taper current during absorption and float phases to ensure longevity.
• Parasitic loads: Dome lights, modules, or accessories drawing power while charging extend the timeline.

If your battery won’t reach and hold about 12.6–12.8 V after resting off the charger, it may be nearing end‑of‑life, not merely undercharged.

Safety and good practice

Correct setup protects both you and the battery while optimizing charge time.

• Use a modern smart charger matched to your battery chemistry (flooded, AGM, EFB, lithium).
• As a rule of thumb, limit charge current to about 10–20% of the battery’s Ah capacity unless the manufacturer allows more.
• Charge in a ventilated area; flooded batteries can vent hydrogen gas.
• Do not fast‑charge if the battery is below freezing; warm it first.
• Clean and tighten terminals; poor connections slow charging and create heat.
• If jump‑started, drive for at least 30–60 minutes to recover some charge, but use a charger to finish the job and avoid alternator stress.

These steps improve safety and reduce the chance of damaging a marginal battery—or your vehicle’s charging system.

EV Traction Battery: From Home Charging to DC Fast

High‑voltage EV batteries are measured in kilowatt‑hours, so time depends on both battery size and charger power. Charging also tapers as you approach full, which is why “10–80%” is quoted more often than “0–100%.”

Typical times by charging level

Here’s how long most modern EVs take under common scenarios, assuming mild temperatures and a healthy battery.

• Level 1 (120 V, ~1.2–1.4 kW): Adds roughly 3–5 miles of range per hour; 10–100% on a 60–100 kWh pack can take 40–70+ hours. Best for topping up, not full charges.
• Level 2 (240 V, ~7–11 kW): Typical home/work chargers. Many EVs go 10–100% in about 6–12 hours; 10–80% in ~4–8 hours, depending on onboard charger capacity.
• DC fast charging (50–350 kW): Most current EVs charge 10–80% in about 18–45 minutes under ideal conditions. From 80–100% can add another 20–60 minutes due to tapering. Peak rates and curves vary by model and station.

Real‑world times depend heavily on your vehicle’s charging curve, station capability (150 kW vs 350 kW), preconditioning, battery size, and starting state of charge.

What affects EV charging time

Even on the same charger, two EVs can finish hours apart because of their hardware and software.

• Battery size: Bigger kWh takes longer at the same power.
• Onboard AC charger: Limits maximum Level 2 rate (often 7.2–11.5 kW).
• Peak DC rate and charging curve: Some cars sustain high power longer; others taper early.
• Temperature and preconditioning: Warmed batteries accept higher power; cold packs charge slowly.
• SOC window: The last 20% slows considerably to protect the pack; 10–80% is the fastest slice.
• Station limits and sharing: Older or shared cabinets may deliver less than advertised power.
• System voltage: 800‑V architectures can leverage 350‑kW stations more effectively than 400‑V systems.

Planning tools in most EVs and major charging apps can predict stop durations based on your route, temperature, and charger type, providing a more precise expectation than generic times.

How to Estimate Your Charge Time Quickly

A few quick calculations give you a realistic window for both 12‑V and EV batteries.

1. 12‑V battery: Estimate amp‑hours needed (capacity × percent to refill). Time ≈ (Ah needed ÷ charger amps) × 1.2–1.4. Example: 60 Ah at 40% (needs 36 Ah) on 6 A → (36 ÷ 6) × 1.3 ≈ 7.8 hours.
2. EV battery (AC Level 2): Time ≈ kWh to add ÷ charger kW. Example: Add 40 kWh on an 11 kW charger → ~3.6 hours (plus minor overhead).
3. EV battery (DC fast): Use the car’s projected 10–80% time for your model; add 20–60 minutes if you truly need 100% due to tapering.

These estimates are close enough for planning, but always allow extra time for cold weather, aged batteries, or shared charging equipment.

Summary

For a 12‑volt car battery, expect roughly 4–8 hours on a 10 A smart charger, 8–12 hours at 6 A, and 24–48+ hours on a 1–2 A maintainer; driving can recover a partial discharge in 30–120 minutes but won’t reliably achieve a full, gentle top‑off. For EV traction batteries, Level 2 home charging usually takes 6–12 hours to reach full, while DC fast chargers bring most cars from 10–80% in around 20–40 minutes, with the final 20% taking significantly longer. Temperature, battery health, and charger capability are the biggest swing factors—so use the quick formulas here to tailor the timing to your setup.

Is 30 minutes enough to charge a car battery?

Driving your vehicle is one way to recharge your car battery. The automotive experts at CAA Auto Advice say that driving your car for 20-30 minutes will help. Short distance trips may not be enough to get a full charge so be sure to check your driving time.

Does a car battery get charged while idling?

Yes, a car battery does get charged while the engine is idling, but it is a much slower and less efficient process than driving because the alternator produces less power at low RPMs. The alternator converts the engine’s rotational energy into electricity to charge the battery and power the car’s accessories, but at idle, there is less power available, and it can take hours to fully charge a depleted battery, especially with electrical components like the radio or headlights turned on. 
Why it’s slow

• Low RPMs: Opens in new tabWhen a car is idling, the engine is not spinning as fast as when it is driving, which means the alternator is not operating at its full capacity. 
• Electrical Load: Opens in new tabModern cars have many electronic systems that consume power, and the alternator’s low output at idle may not be enough to charge the battery if these accessories are running. 
• Energy Imbalance: Opens in new tabThe energy needed to start the engine is significantly more than what the alternator can replace by idling. 

What happens when you idle

• Some Charge is Generated: The alternator still produces some voltage, so the battery receives a small charge. 
• Battery Gradually Depletes: Without enough charge being replaced, especially if the battery is already low or with accessories on, the battery will slowly decline over time. 
• Not a Quick Fix: Idling is not an effective way to quickly charge a dead battery. 

Better alternatives

• Drive the Car: Opens in new tabDriving at higher RPMs is the most effective way to allow the alternator to generate more power and quickly recharge the battery. 
• Minimize Electrical Use: Opens in new tabWhen idling for a short period to charge, turn off as many non-essential accessories as possible. 
• Use a Battery Charger: Opens in new tabFor a more efficient and reliable charge, especially if the battery is severely discharged, using a dedicated battery charger is the best option. 

How long should I let a completely dead car battery charge?

Charging a dead car battery can take anywhere from about 1 hour with a high-output smart charger to over 12 hours with a basic linear charger, or even 3-4 days with a trickle charger. A fully dead battery will require the longest charging time, while a partially discharged battery will charge faster. For a deeply discharged battery, driving for about 30 minutes to an hour at highway speeds can provide a sufficient charge to restart the car, but a dedicated charger is recommended for a complete and safe charge. 
Factors affecting charging time:

• Charger type: Opens in new tabDifferent chargers have varying output rates. A multi-stage or smart charger will charge faster than a simple linear charger. 
• Battery capacity: Opens in new tabThe amp-hour rating of your battery affects the total charge time needed. 
• Battery condition: Opens in new tabA completely dead battery takes longer to charge than one that is only slightly discharged. 
• Driving conditions: Opens in new tabA car’s alternator can charge a battery, but it’s less efficient than a dedicated battery charger and can take hours of driving to fully charge a deep-discharge battery. 

How to charge a dead battery:

1. Use a battery charger: Connect the positive (red) terminal of the charger to the positive (+) terminal of the battery and the negative (black) terminal of the charger to the negative (-) terminal. 
2. Select the right charger setting: Choose the correct setting for your battery type, such as AGM or lithium ion, and consider the battery’s amp-hour rating to match the charger’s output. 
3. Allow sufficient time: Allow the charger to complete its cycle, especially when charging a deeply discharged battery, to ensure a full and safe charge. 

This video explains how to charge a dead car battery: 53sCTEK Battery ChargersYouTube · Sep 25, 2024
Important considerations:

• Battery health: If the battery is very old or has been deeply discharged for a long time, it may no longer be able to hold a charge. 
• Safety: Always follow the instructions for your specific charger and be careful to avoid touching any metal surfaces when connecting or disconnecting jumper cables, according to this guide from Mercedes-Benz of Daytona Beach. 

How long does it take to fully charge a vehicle battery?

Depending on your battery charger, it may take 4-8 hours to charge your battery enough to start the car a few times. It may take 10-24 hours to charge your battery up to 100%. The longer you charge it, the more strength the charger can put in the car battery.