How To Wire Two Batteries In A Car

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Do you want to know how to hook up two batteries in a car? Almost every owner of a car knows the role a car battery plays in the system of a car. Its role is to provide electricity that’s necessary to start the engine of a car. When you’re driving a car, the electricity is provided by the generator. While providing the electricity, the generator also charges the car battery of a car. At the same time, when the engine of a car is shut off or there is a case of idle speed, the margin of energy is not replenished. It’s used by those devices of a car that need it. It’s important to point out that the number of such like devices installed in modern cars is increasing. That’s why many car owners become interested in installing a second battery in their car.

installing two batteries in a car

Who May Need A Second Battery In A Car And Why May It Be Needed?

When it comes down to those who may need to install two batteries in a car, the first group of persons that comes to mind is the group of those who own off-road vehicles with an electric winch. It becomes more and more common nowadays to see various devices in a car that consume energy. For example, a refrigerator, a heating unit, a laptop, a DVD player, a microwave oven and even a coffeemaker. Besides, is you have an additional car battery in your car, you may install an anti-theft system, an alarm system and radio in it. If you have a good car audio system, you should know that it also consumes lots of energy.

how to hook up two batteries in a car

So the answer to the question mentioned above is quite simple – a second battery in the car is needed if the main car battery can’t provide enough energy for all the devices in a car that consume energy.

How Do You Find Out Whether It’s Necessary To Hook Up Two Batteries In A Car?

Everything is quite simple here. Let’s say you have a car battery with the capacity of 60-65 Ah. The approximate discharge capacity of such like a battery amounts to 4 kW. The devices you have in your car consume approximately 2 kW. It means that if you decide to install any additional devices in your car, the total input power of which will amount to more than 2 kW, you’ll need to think over the possibility of installing an additional car battery. As for the input power of different devices, you may find out about it if you read through the instructions or manuals that you’re provided with when buying any devices.

running two batteries in a car

Useful Tips On Installing Two Car Batteries

  • – You shouldn’t install an additional car battery in your car. The thing is that when it’s functioning, it sends off fumes that may be dangerous for passengers in your car. As a rule, a second car battery is installed in a car’s trunk.
  • – Pay attention to the capacity of the generator. It will be better to have a high capacity generator. The higher it is, the faster will it be able to replenish the charge level of both the batteries.
  • – Some experts say that it’s better to install a second battery that has the same capacity as the first one. If the batteries have different capacity, it results in one of them gradually discharging the other one. At the same time, there are those who disagree with this theory. You are free to decide what to do here.
  • – When choosing an additional battery, you need pay attention to whether the second battery can stand lots of discharge-charge cycles. If you connect a number of devices that consume energy to it (car audio system, refrigerator etc.), it will discharge fast and very often.

How To Wire and To Connect Two Batteries In A Car. 3 Methods

The 1st Method: Installing Two Car Batteries In Parallel

Below you can see the scheme of the method. It is the easiest and the simplest method to use. You only need to connect the positive battery terminal with the positive one and the negative battery terminal with the negative one. After it, you may start using your car.

How to wire two batteries in a car

Useful tip: it’s recommended to install protectors on the distance of 16 inches from the positive battery terminal. You should install a protector on the distance mentioned for the main and additional car battery.

However, the method also has some disadvantages.

The main problem that you may face is that all the devices consuming electricity are connected to the main car battery. Consequently, the electric energy from the additional car battery will pass through the main battery before it’s provided to the devices. Therefore, you spent the energy supply of the first car battery. The supply is then replenished with the help of the additional car battery. It also means that the generator will charge the main car battery first. Only then, it will charge the second car battery. Such like cycles of charge-discharge decrease the service life of both the car batteries. That’s why you need to read through the information on the 2nd method of wiring two batteries in a car.

The 2nd Method. Installing The Second Car Battery With A Diode Battery Isolator

This method implies that you need to connect a car battery to the network system of a car through a battery isolator. It will pass current in one direction. It’s meant to isolate the on-board network of a car and the additional car battery. Such like devices have different designs and they may connect several car batteries.

how to wire a second battery in a car

If you use the method described, the additional electricity consuming devices will be connected to the second car battery. It means that you’ll be able to watch TV, play games on the laptop and turn the heating unit on while having the main car battery fully charged and being able to start the engine. When driving your car, both the car batteries will be charging from the generator.

This method also has disadvantages. If the devices consume lots of energy, the 2nd car battery will get discharged fast. Consequently, you’ll need to charge it before using the devices.

The 3rd method. Connecting the car batteries in one net.

Nowadays, there are devices that allow you to manage several car batteries connected in one net. You may either manage them manually or turn the auto-mode on. The method implies that the system network of a car uses the electricity of 2 (or more) car batteries. If the voltage rate in one of the car batteries decreases, the device will use the electricity from the other one. The batteries are charged according to the same principle.

how to install a second battery in your car

Such like devices allow you to manually choose the battery you want to use at the moment. There are models of the devices that notify you of the low charge level of the batteries and turn some electricity consuming devices off. There are devices that have special indicators to be installed inside your car. They help a car owner see the level of a car battery charge.

One of the most popular devices are Whisper Power devices that can work with the current capacity of 120-160 A. The capacity depends on a model. The company also offers WBI battery isolator that allow you to connect several car batteries to your car. You can also find the devices manufactured by the company Victron Energy in the market.

We hope the information provided is useful for you. If you have questions left, you can write them in the comments.

One comment

  1. I’ve recently installed the 2nd car battery on my car. Everything is great. Now I can stop worrying about what happens in case the 1st battery gets discharged.

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