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Battery System

How to Charge a Car Battery Without a Charger? – 4 Methods

How to Charge a Car Battery Without a Charger
Last Updated on Aug 16, 2023 By Lillian Kazmierczak

The biggest fear of every car owner becomes a reality when the car runs out of charge. The dashboard will notify you if your battery is at a low charge if you drive it frequently.

But it is possible that you didn’t notice the warning sign, ignored it, or didn’t start your car for days. You may have a low or dead battery for various reasons. The charger may not be readily available to you, so you need to know how to charge a battery without one.

How to Charge a Car Battery Without a Charger

Method 1 – Charge with jump leads

The only way to start your car when your battery is flat is to jump-start it. With the engine started, you can drive to where you’re going, and then use a charger to charge your car. Jumper cables from another car must be connected to your battery to jump-start it.

Your battery can be charged enough by the jump leads to start your vehicle. Jump leads will not work if the battery is faulty. You should read your car’s booklet to ensure that the jump leads are connected correctly. Failure to do so can damage the battery. Be sure to follow these steps.

Step 1: Make sure there is nothing dirty, rusted, or corrosion on the battery terminals by cleaning them with a wire brush. You must do this before connecting the jump leads to ensure proper charging.

Step 2: In order for the current to flow safely and steadily. Make sure the jump leads don’t exceed 6 gauge.

Step 3: The donor car must be on and running for a few minutes with the leads attached to your battery to allow enough charge to turn the engine over.

Method 2: Charge with a laptop charger

Laptop chargers can be used to charge car batteries. A laptop charger can be used at home or in an emergency to charge your car battery; no jumper cables are needed.

Laptop batteries usually have 19V, while cars use 12V batteries. That means the laptop charger can be used to charge 12V batteries.

Requirements for charging a car battery with a laptop charge:

  • Car battery
  • Jumper wires
  • Digital voltmeter
  • Laptop charger
  • Digital multimeter

You should properly connect the laptop charger to the dead car battery so as to use it as a laptop charger. It’s for this reason that you need to make a proper connection.

Step 1: Connect the wires

The first thing you need to do is remove the battery. A clean, dry surface should be used for your car battery.

In order to charge your laptop, you need to plug it into an outlet at home. The negative terminal of the battery should be connected to the negative cable.

Using the positive cable, connect the multimeter to the positive terminal of your battery. (A positive cable or wire is attached to the multimeter so the reading can be seen on it).

Step 2: Charge the battery and note the voltage

Once the battery is connected to the laptop charger, you can measure the voltage and current on the digital multimeter. Again, do this once the battery has been charged.

A laptop charger will charge your battery in 4-6 hours.

Step 3: Test the battery and finish up

Wait around 4 hours and then measure the voltage and charge of your battery. Place the battery back in your car if recharged.

Using a laptop charger to charge a car battery is not common but does work. Car batteries should always be charged with a charger because it’s the safest and most effective way to do it.

Method 3: Charge with a home inverter

Home inverters aren’t well known for charging up car batteries. Using this method rarely is okay, but not frequently

This method involves converting the alternative current (AC) delivered by a wall socket into direct current (DC) produced by a battery.

Step 1:

Before setting up the connections, disconnect the inverter from your power source, plug the negative battery port into the black inverter jack, and plug the positive battery port into the inverter’s positive port.

Step 2:

Make sure the connections are as described above. Now the inverter needs to be plugged into the wall.

Step 3:

Since inverters provide high power, it may take up to 3 hours for the battery to be fully charged, so it’s best not to use this method if you don’t have time.

Method 4: Charge by putting the battery into a different vehicle

In the case of a flat battery without a charger, find another car with a battery that is similar to your flat battery then you can charge your battery with that.

This method is less effective if you don’t have a battery car charger. The technology is most useful for older, simpler vehicles with simpler electrical systems. However, it can be used to charge car batteries in RVs or campsites.

  • Make sure the dead battery matches the other car’s size and shape.
  • Make sure the dead battery and the donor vehicle have the same mAh rating.
  • Using a donor vehicle to charge a dead battery, jump-start the car after installing the dead battery.
  • For this process to be successful, turn off every auxiliary electricity source and the engine of the car. Following this precaution, the donor’s car can be fitted with the dead battery.
  • In the event that the battery is dead, the alternator will revive the dead battery by jump-starting the car.
  • As soon as the dead battery is placed in the car, start the engine and run it for 20-30 minutes) or go for an easy drive to charge the battery completely.


1. Can I charge my battery with a battery isolator?

Ans. To charge a secondary battery, a battery isolator drives the alternator charge of the main battery.  It may not be the most efficient method, but it can accomplish the task. Trying to revive a dead battery might be tough, but it’s worth a shot. Alternators charge primary batteries first and then supply power to battery isolators to charge secondary batteries. For RVs and campsites, battery isolators are quite common.

2. Can a fully dead battery be recharged?

Ans. Yes, if the battery is completely dead, it can be recharged via one of the ways we have mentioned. It may take longer if the battery has sat dead flat for weeks.

About the author

Lillian Kazmierczak

As far as I can remember, I would say I have been a car nut for my whole life. My father was a car dealer who used to change and repair his cars himself. This gave me the opportunity to get around all sorts of cars and get my hands dirty repairing vehicles from an early age.

A great fan of Japanese quality and German preciosity, my deep passion lies in older models that I believe have a flair that takes me back to my childhood! I also love their extraordinary durability and reliability when compared to today’s modern models.

When not out taking a ride, I enjoy socializing with fellow motorheads online and consuming any car facts and figures I can get my mind on!

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