How can I get my car battery to charge?

You can charge a car battery using a dedicated 12-volt charger, by jump-starting with another vehicle or a booster pack, or by driving to let the alternator recharge the battery. These methods vary in speed and suitability depending on the battery’s age and condition.

In this guide you’ll find safe, practical steps for charging a discharged battery, how to choose the right method, and tips for diagnosing why a battery may not hold a charge. Whether you’re dealing with a dead battery on a cold morning or trying to minimize future failures, these steps help you get back on the road responsibly.

Immediate charging options

The following options cover the most common ways to bring a depleted battery back to life. Each option has its own setup and safety considerations.

• Use a dedicated 12V battery charger or a smart charger designed for automotive batteries, following the manufacturer’s instructions.


• Jump-start with another vehicle or a portable booster pack, using proper polarity and safety procedures.


• Drive the car to recharge via the alternator, if the battery isn’t severely damaged and you can safely do so.


• Use a portable jump starter as a quick interim solution when another vehicle isn’t available.

Choose the option that matches what you have on hand and your battery’s condition, and monitor the battery and electrical system for overheating, smells, or abnormal behavior during charging.

Charging methods explained

Different batteries and situations call for different approaches. The sections below walk you through each common method with practical steps and safety notes.

Using a dedicated 12V charger

Before you start, ensure you know your battery type and the charger's compatibility. Use a charger with automatic shutoff and, if possible, temperature compensation and a smart charging sequence.

1. Park the vehicle on a flat, well-ventilated surface and turn off the engine and all accessories.


2. Open the hood and locate the battery terminals; identify the positive (+) and negative (−) posts.


3. Connect the charger's red clamp to the battery's positive post, then connect the black clamp to a solid metal ground on the vehicle (or the negative post if no alternative is available).


4. Set the charger to 12V and choose a charging rate appropriate for the battery's capacity (typically 2–4 amps for a standard car battery; higher rates may be used for faster charging if the battery and charger support it).


5. Power on the charger and let it run until the battery reaches full charge according to the charger's display (often indicated by a full-charge or “0% rate”/float stage).


6. Turn off and unplug the charger, then remove the clamps in reverse order (black first, then red) and close the hood.


7. Test the battery with a voltmeter; a fully charged 12V lead-acid battery should read about 12.6V to 12.8V when resting.

After charging, allow the battery a few minutes to settle, then attempt to start the vehicle to confirm it will run reliably. If it won’t hold a charge or the voltage drops quickly, the battery or the charging system may be faulty and professional testing is advised.

Jump-starting with another vehicle or booster pack

Safety first: use correct polarity, ensure clamps are insulated, and keep metal parts away from the battery to avoid sparks. If using a booster pack, follow the manufacturer’s instructions since packs vary in design.

1. Position both vehicles safely with engines off. Identify the positive (red) and negative (black) terminals on both batteries.


2. Connect the red clamp to the positive terminal of the dead battery, then connect the other red clamp to the positive terminal of the donor battery or booster pack.


3. Attach the black clamp to the negative terminal of the donor battery, then connect the other black clamp to a solid, unpainted metal surface on the engine block or chassis of the vehicle with the dead battery (not to the dead battery’s negative terminal).


4. Start the donor vehicle and allow it to run for a few minutes, then try starting the dead vehicle. If it starts, let it run and drive to recharge the battery.


5. Disconnect the cables in reverse order: black from the ground point, black from the donor battery, red from the donor/battery, and red from the dead battery.

If the dead vehicle doesn’t start after several attempts, the battery may be beyond jump-start, or there could be an issue with the alternator or starter. Do not crank for extended periods; allow brief pauses between attempts.

Charging by driving (alternator recharge)

Running the engine can help recharge a battery through the alternator, but this should not be the sole method for a deeply discharged battery. Safe driving and a healthy charging system are required for this approach.

1. Drive at a steady pace, preferably on a highway or longer stretch of road, for about 20–30 minutes or longer if needed to restore charge.


2. Avoid frequent short trips after a discharge; if possible, combine errands into one longer trip to give the alternator time to replenish the battery.


3. If the battery fails to hold a charge after a road trip or shows signs of weakness, have the charging system and battery tested professionally.

Note: This method relies on a healthy alternator and no significant parasitic drain. If you suspect either problem, seek professional service rather than relying on driving alone.

Battery health and maintenance

Charging is only part of the picture. Batteries age and lose capacity over time. Here’s how to assess and maintain battery health to minimize future charging problems.

• Aging and capacity loss: Most car batteries last 3–5 years under normal use; performance declines with temperature and recharge cycles.


• Signs of a failing battery: slow cranking, dim headlights, or frequent false alarms about power; swollen or leaked batteries require immediate attention.


• Testing and load checks: have a professional perform a load test or use a reputable battery tester to assess reserve capacity and cold-cranking amps (CCA).


• Parasitic drains: electronics left on or aging modules can drain a battery while the car is off; diagnosing drains requires careful testing and sometimes professional help.

Replacement is often the most reliable solution for an old or failing battery. Regular maintenance, proper charging practices, and avoiding deep discharges extend life and reliability.

Safety reminders

Charging car batteries involves the risk of acid exposure, gas buildup, and fire or explosion if mishandled. Always wear eye protection and gloves, work in a well-ventilated area, keep flames and sparks away, and follow manufacturer instructions for any charger or booster device.

Troubleshooting: when charging doesn’t work

If charging fails to restore functionality, use these steps to diagnose the issue and decide on the next action.

1. Test battery voltage with a multimeter to confirm resting voltage and charging current.


2. Perform a load test to see if the battery can hold voltage under load.


3. Inspect the alternator belt, connections, and charging output to ensure the alternator is charging the battery properly.


4. Check for parasitic drains by inspecting fuses, modules, and wiring for unintended power draw when the vehicle is off.


5. Inspect battery terminals for corrosion or loose connections; clean and tighten as needed.


6. Consider professional testing if results are inconclusive or the charging system continues to fail after these checks.

If issues persist, the battery or the vehicle’s charging system may require replacement or repair by a qualified technician.

Summary

To get your car battery charged, choose a method that matches your situation: a dedicated charger for controlled charging, a safe jump-start or booster pack for rapid revival, or a drive to leverage the alternator’s charging power. Follow proper safety procedures, account for your battery type and age, and monitor performance after charging. If a battery repeatedly fails to hold a charge, replacement or professional inspection of the electrical system is usually the prudent course of action.

What to do if a car battery won't charge?

To fix a car battery that isn't charging, first clean corroded terminals and then use a multimeter to check the alternator's output voltage while the engine is running, which should be around 13.5−14.513.5 minus 14.513.5−14.5 volts. If the voltage is too low, the alternator or a related fuse, belt, or wiring issue is likely the cause; if it's too high or the battery is old, the battery itself may need replacing. 
This video demonstrates how to check for parasitic draw to troubleshoot a car battery not charging: 1mChrisFixYouTube · May 6, 2021
1. Clean the battery terminals 

• Corrosion on the terminals can block the flow of electricity. 
• Disconnect the battery cables. 
• Use a wire brush and a mixture of baking soda and water to scrub the terminals and cable clamps until they are clean. 
• Securely reconnect the cables to the terminals. 

2. Test the alternator and charging system 

• Start the car and use a multimeter to measure the voltage at the battery terminals.
• The reading should be between 13.513.513.5 and 14.514.514.5 volts.
• If the voltage is below 13.513.513.5 volts, the alternator is not charging the battery correctly. 

This video explains how to test if your car's alternator is working correctly: 53sChrisFixYouTube · May 14, 2014
3. Address potential causes

• Blown fuse: Check the fuses for the charging system and replace any blown ones with the same amperage rating. 
• Loose or damaged alternator belt: A slipping or broken belt can prevent the alternator from spinning and charging the battery. 
• Wiring issues: Inspect the wires connected to the alternator and battery for any loose connections or damage. 
• Alternator failure: If the voltage is low, the alternator may need to be replaced. 

4. Consider other possibilities

• Old battery: If the battery is more than five years old, it may have reached the end of its life and needs to be replaced. 
• Parasitic drain: A component in the car may be drawing power even when the car is off, which can drain the battery. A professional can test for this. 
• Deeply discharged battery: If a charger doesn't seem to recognize a deeply discharged battery, you can temporarily use jumper cables to connect it to a working car to give it a small surface charge before using the charger again. 

You can watch this video to learn how to revive a completely dead car battery that won't charge: 41sDylan KowalskiYouTube · Mar 5, 2023

Can a completely dead car battery be recharged?

Yes, a completely dead car battery can often be recharged, but the best method is using a suitable battery charger to ensure a full and safe charge. Jump-starting and driving the car may work for a slightly depleted battery, but it can be ineffective for a completely dead one and can damage the alternator over time if done frequently. 
This video explains how to charge a dead car battery using a charger: 57sInspiring BuildsYouTube · Aug 17, 2024
Using a battery charger (recommended)

• Method: Connect a compatible battery charger to the battery and plug it in. A charger with a "smart" or "maintainer" function that includes a desulfation mode is best for a deeply discharged battery. 
• Time: This can take up to 24 hours or more, depending on the charger's amperage and the battery's condition. 
• Safety: Always follow the charger's safety instructions and ensure the battery has no cracks or leaks before charging. 

Jump-starting and driving (less effective for a truly dead battery) 

• Method: Use jumper cables to connect your dead battery to a working vehicle, start the working car, and then attempt to start the car with the dead battery. 
• Limitations: If the battery is completely dead (zero volts), the car's alternator may not have enough power to charge it effectively while idling. A long drive at speed is better, but it may not be enough to fully restore a deeply discharged battery. 
• Risk: Repeatedly jump-starting a deeply discharged battery can strain the alternator and cause it to fail prematurely. 

Before you start

• Inspect the battery: Before attempting to charge, check the battery for any physical damage like cracks or leaks. 
• Clean terminals: Clean any corrosion from the battery terminals to ensure a good connection. 
• Use a charger if possible: The safest and most effective way to recover a deeply discharged battery is with a proper charger. 

How do you manually charge a car battery?

Car. Starts so in removing the cables. Now what you want to do is go in the complete opposite. Direction. So start with the live red terminal from the car you just started and take that one off.

Does idling your car charge the battery?

Yes, idling a car charges the battery, but it is very inefficient. The alternator generates a small amount of electricity at low RPMs, which may not be enough to both power the car's electronics and significantly charge the battery. Idling for a short period is unlikely to fully recharge a dead or weak battery and could even cause a slow drain if electrical loads are high. Driving the car for 20-30 minutes is a much more effective way to charge the battery. 
This video explains the basics of how a car's charging system works: 58sMore AutomotiveYouTube · Oct 30, 2025
Why idling is inefficient

• Low RPMs: The alternator, which generates the electricity, spins slower when the engine is idling. This produces less power compared to when the engine is at higher, driving speeds. 
• Power drain: The engine's electrical components, such as headlights, radio, and air conditioning, constantly draw power. At idle, the alternator may only produce enough power to meet these demands, leaving little to no excess to charge the battery. 
• Not enough for a dead battery: If a battery is significantly depleted, such as after a jump-start, idling will not provide enough charge. It can take hours of idling to get a small amount of charge, while driving for 30 minutes is much more effective. 

This video explains why idling is not an efficient way to charge a car battery: 52sCar Performance ProsYouTube · Jan 6, 2025
How to charge the battery effectively

• Drive the car: The best method is to drive the car for at least 20-30 minutes. This increases the alternator's output and allows it to properly recharge the battery. 
• Use a dedicated charger: For a deeply discharged battery, a dedicated battery charger or jump-starter is the most efficient solution. A trickle charger can also be used to maintain a healthy battery, especially if the car is not used frequently. 
• If you must idle: If you have no other option than to idle, turn off all unnecessary accessories to reduce the electrical load. You can also slightly increase the engine's RPM by revving the engine to make the alternator produce a little more power.