How Long Does It Take to Charge a Car Battery & Why?

Car batteries often fail at the worst possible times, leaving you stranded and frustrated.

Whether it’s from leaving your lights on overnight or letting your car sit idle for weeks, a flat battery is always inconvenient.

So, how long does it take to charge a car battery?
Car battery charging times can vary based on factors like the type of charger, its amperage, and the battery’s condition.

Let’s find out what influences battery charging time, why it takes so long to recharge it, and how to recharge safely.

This Article Contains:

How Long Does It Take to Charge a Car Battery?
How Long Does It Take to Charge a Car Battery While Driving?
Why Do Car Batteries Take So Long to Charge?
How to Charge a Car Battery the Right Way
4 FAQs about Recharging Car Batteries

How Long Does It Take to Charge a Car Battery?

Charging a battery can take 4 to 8 hours with a standard 12-volt charger. However, this can vary depending on the car battery charger type and its amperage.

Let’s break it down:

1. Charger Amperage

A car battery typically has a capacity of around 48 amp-hours (Ah). To estimate how long it’ll take to charge, divide 48 by the amp rating of your battery charger.

For example:

Two amps: 24 hours
Six amps: 8 hours
Eight amps: 6 hours
Ten amps: 5 hours

2. Charger Type

Here are some common types of chargers and their battery charging time:

Standard or linear chargers: These provide a continuous battery charge and take 4 to 12 hours to fully recharge a car battery. However, they lack an auto-shutoff feature, so there’s a risk of overcharging and potential battery damage.

Smart battery chargers: They monitor battery voltage and adjust the charging rate. They take 10 to 24 hours to fully charge and can detect the battery type (AGM battery or lead-acid battery) to apply the correct settings.

Multi-stage chargers: They’re designed for safer charging and operate in three stages (bulk, absorption, and float). Some models of this fast charger can fully recharge a battery in as little as one hour while preserving battery life.

Trickle chargers: They operate at low amperage (1-2 amps), provide slow charging, and can take 3+ days to charge a weak battery.

NOTE: Additional factors like battery capacity, size, and weather conditions can also influence charging speed. Larger batteries with higher capacities generally take longer to charge. Similarly, cold weather slows the battery’s chemical reactions, increasing its charging time.

Can driving recharge your car battery?
Let’s find out.

How Long Does It Take to Charge a Car Battery While Driving?

It usually takes 4 to 8 hours of driving at highway speeds to partially recharge a car battery, and the engine must run at a minimum of 1,000 RPM (revolutions per minute).

However, driving alone won’t fully charge the battery. When your battery is drained, the alternator recharges it while you drive. But its main job is to power your car’s electronics, such as the AC, headlights, and onboard systems.

Moreover, the idea that a 30-minute drive will fully recharge a battery is outdated, especially with the higher power demands of modern vehicles. For a full recharge, it’s best to use a dedicated car battery charger.

TIP: If you don’t drive your vehicle often, consider using a battery maintainer. These devices monitor the battery’s voltage and supply enough power to maintain its charge.

Now that we know how long it takes to charge a battery using a charger or while driving, let’s understand why it takes that long.

Why Do Car Batteries Take So Long to Charge?

Car batteries charge slowly to prevent overheating, which causes the water inside them to evaporate. This can make the battery acid more corrosive and lead to faster wear.

To avoid this, smart and multi-stage chargers regulate power delivery to the battery using a controlled three-stage charging process:

Bulk phase: It charges the battery to about 75% without significantly increasing the voltage to prevent overheating.
Absorption phase: The remaining 25% is charged slowly, with the charger carefully raising the battery’s voltage to get it to 12 volts.
Float phase: Keeps the battery voltage up until you remove the charger. Once it’s charged to 100%, it turns into a trickle charger to maintain the battery charge.

This charging process ensures the battery replenishes safely and lasts longer, but it can take 10 to 24 hours or more.

Next, let’s understand how to recharge your battery safely.

How to Charge a Car Battery the Right Way

If you’re new to battery parts, don’t have access to a charger, or are dealing with a damaged battery, it’s better to call a professional mechanic for help.

If you plan to do it yourself, here are the step-by-step instructions to recharge your battery:

CAUTION: Before charging, inspect the battery for physical damage (e.g., bulges, cracks, or leaks) and ensure it’s safe to recharge. A damaged battery shouldn’t be charged. Also, ensure the area is well-ventilated.

Park the car and connect a backup battery to the OBD-II port to prevent system resets and power the car’s computers.

Clean any corrosion or dirt from the battery terminals using a wire brush before attaching the charger clamps.

If using a linear charger, disconnect the negative battery terminal and leave the positive terminal connected to prevent electrical surges. Cover the negative terminal with a rag to avoid accidental contact with any metal part.

NOTE: For smart or multi-stage chargers, you can leave the battery terminals connected because the chargers are designed to regulate voltage and prevent surges.

Attach the charger clamps to the battery terminals (positive to positive and negative to negative), ensuring no contact between the clamps and the negative terminal.
For a linear charger, select the battery type — “wet” or “flooded” mode for standard batteries and set the voltage to 12 volts. If it’s a smart charger, it’ll automatically detect the correct settings.

Monitor the charger’s indicator. Depending on the battery capacity and condition, partial charging may take 4 to 8 hours, while a full charge can take 10 to 24 hours.

Once the battery is fully charged (around 12.88 volts), unplug the charger and carefully remove the clamps without touching the loose negative cable.

Securely reattach the negative battery terminal and remove the backup battery from the OBD-II port. Check all connections to ensure the car starts without issues.

Got more questions?
Check out these FAQs.

4 FAQs about Recharging Car Batteries

Here are the answers to common questions about charging car batteries:

1. When Should You Recharge Your Car Battery?

It’s time to recharge your car battery if:

The car is starting slower than usual
You hear odd clicking noises on turning the ignition key
The car’s accessories, like the radio or lights, stop working
You recently had to jump-start your vehicle
You left interior lights on overnight, and now the car struggles to start

2. How Long Will It Take to Charge a Dead Car Battery?

Charging speed depends on your battery size, type, and charger. For a completely dead battery, it’s best to charge it overnight at a low amperage. Increasing the charging rate can strain the battery cells and increase the risk of damage.

3. Can You Charge a Battery While Idling?

No, idling doesn’t charge a car battery. It only generates enough charging current to power the car’s electronics.

4. How Long Does It Take to Charge an EV Battery?

Electric vehicles typically use a rechargeable lithium-ion battery, and EV charging times can vary depending on the type of charging station used:

Level 1 chargers (home charging point): These provide slow charging, which takes about 40 hours to recharge an electric car battery.

Level 2 chargers: These add 15 to 25 miles of range per hour and can recharge an electric car battery overnight, making them ideal for home or workplace use.

Level 3 or DC fast charging: These chargers, found at public charging stations, can recharge a lithium-ion battery in 30 minutes.

Solve Battery Problems with AutoNation Mobile Service

While recharging can revive a weak battery, knowing when a replacement is necessary is just as important. If your car battery is over 5 years old, recharging it may no longer be effective. In such cases, replacing the battery is the most reliable solution to avoid unexpected breakdowns.

If you’re unsure, AutoNation Mobile Service can help!

We offer hassle-free battery checks and replacements right from your driveway, saving you a trip to the repair shop. We also provide upfront pricing and a 12-month, 12,000-mile warranty on all repairs.