Charge car battery: Step by step guide

How to change a car battery?

Do you need to charge your car battery and wonder how to do it? Do not know which pole to connect first? Then you have come to the right place!

Here I go through what you should keep in mind when charging your car battery and how to connect.

There are some things that can be good to keep in mind when connecting a charger to your car battery.

We start with how you know the difference between plus and minus.

Change car battery

Plus (red)

Plus is almost always in some way marked with red color.

The cable and / or connector for your battery charger’s positive cable is usually red.

The positive pole of the battery is marked with a plus sign (+) and sometimes even red in some way.

If you buy a new battery, the positive terminal, for example, usually has a red plastic lid as protection.

Minus (black)

Minus almost always has a black cable and / or plug.

I have on occasion occasionally come across car batteries where the negative pole is marked in blue.

The negative terminal of the battery is always marked with a negative sign (-).

Things to consider before connecting the charger

Here are some things to keep in mind before recharging your battery.

Read the battery maintenance tips here >>

Use the correct battery charger

First and foremost, make sure you have the right type of charger for your battery and that the charger is set up correctly.

For example, there are chargers that can charge both 12V and 24V. If it is set to 24V and connected, it can be very wrong and (expensive) damage to your battery and / or electronics in your car.

Think about the battery temperature

The car battery you are charging must not be too hot (above 45 degrees) or frozen.

If it is minus degrees outside, take the battery into the heat. Do not leave it in the car in sub-zero temperatures while charging.

Read how the charger works

Depending on what kind of battery charger you have, it has slightly different lamps, meters and functions.

Read the instruction manual before using the charger so that you understand how it works.

Think about ventilation

The battery needs to “breathe” when you charge it. If the battery is under the hood of your car that is outdoors, there is usually no danger.

But avoid charging the battery in confined spaces without ventilation.

Make sure all connections are clean and nice

Sometimes the poles of the battery get dirty or oxidized. I then recommend that you clean everything before charging the battery.

You can use a wire brush to brush the poles of the battery and also the cables/connections

How to connect the charger to a car battery?

If you are going to disconnect the battery from your car, always start with the negative cable (earth). This reduces the risk of a short circuit.

Keep the charger switched off while connecting it, this way you avoid bumping into the wrong components which can create a short circuit and damage the battery or vehicle/electronics.

How to connect a charger to a car battery

  1. Start with the positive cable (usually the red plug from the charger). Connect it to the positive (+) terminal of the battery.
  2. Then connect the negative cable (black) to the negative terminal (-) of the battery.
  3. Double check that both connections are firmly attached to the battery. You do not want to risk something coming loose and creating a short circuit.
  4. Now start the battery charger.
  5. Read your battery charger and make sure that everything is in order and that the battery is charged. Chargers usually have a green light as an indication, but they differ from charger to charger. Read the instruction manual that comes with your charger.

When you disconnect the charger, do the opposite. Turn off the charger. Then disconnect the negative cable and then the positive cable.

How long does it take to charge a car battery?

With almost all modern battery chargers, you can leave the charger connected to the battery without any danger.

The charger keeps track of when the battery is fully charged and it then switches to maintenance charging when needed.

If you are unsure how your charger works, read the instruction manual before leaving it connected without review!

How long it takes to charge the battery depends on how empty it is, what size of battery you have, temperature and charger.

It usually takes around 10-20 hours to fully charge an empty battery. Read more in your charger’s instruction manual because it differs between different chargers.

How often should you charge a car battery?

How often you need to charge your battery depends mainly on how much you drive.

If you commute 30-40 minutes to work every day, you rarely need to think about charging your battery more than what the car already does when driving.

It can still be a good idea to charge the battery 1-2 times a year so that you are sure that it is never discharged too much. A battery feels best when it is fully charged!

If you drive mostly shorter distances or have the car standing a lot, you may need to charge it more often at regular intervals.

How often / rarely it is depends on how little you use the car and it is difficult to answer.

If you drive very little, there are smart chargers that you connect to the battery in the car. Then you can easily stop in a socket when you have the car parked in the garage, carport or parking lot.

Then the battery is charged automatically and is always charged and ready when you go away!

If the battery light starts to illuminate, it may be a sign that you need to charge your battery.

Frequently asked questions about car batteries

Here I have collected some common questions about charging car batteries.

Can you charge the battery in the car?

With modern batteries and chargers, there is usually no danger of charging the battery when it is in the car. If you have the opportunity, disconnect the battery when charging it to be on the safe side.

Can you charge a car battery in minus degrees?

You should avoid charging the battery with a charger in minus degrees as it is not good to charge frozen batteries.