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What Is the Difference between Parallel and Series Batteries? 

 September 19, 2021

By  Phil Borges

Every electrical circuit consists of batteries that are connected in series, parallel or series-parallel configurations. This is how a circuit is closed. These are three different ways of doing the same thing. The choice of configuration depends on the output you want.

In a series connection, you will connect multiple batteries one after the other till you get the desired output voltage while keeping the amp-hour (Ah) capacity constant. In a parallel connection, you will connect multiple batteries in a way that the voltage is constant but the amp-hour capacity of the batteries is increased.

The first difference is in the way they are connected. In a series connection, the opposite terminals of the batteries are connected in a sequence to increase the output voltage. In a parallel connection, all positives are connected to each other and so are the negatives to increase the system capacity while the voltage remains constant.

Now, all the batteries in a series configuration must have the same capacity rating and voltage. And the way you connect them is that the positive terminal of the first battery is attached to the negative terminal of the second and so on.

In the same way, batteries connected in a parallel configuration should also have the same capacity rating and voltage. And the way you connect them is that all the positive terminals are connected to each other using one set of wires and the same is done with the negative terminals using a different wire.

This stacking up of batteries makes it a battery bank and gives it the capacity to power an application for a longer period of time. This happens because of the increased amperage, which is the strength of the current in the electrical circuit.

But it’s not just about how you connect them. Here are some other things you need to know about series and parallel configurations which will tell you when to use these connections.

Is It Better to Connect Batteries in Series or Parallel

Before we get into which is better (and that is not a multiple-choice option because it varies depending on what kind of end result you want) let us look at another important aspect—charging.

Sooner or later, all batteries need to be charged, right? Now, when you are trying to charge batteries that are connected in a series configuration, you need to get a charger that will match the system voltage of the batteries because that is the variable in this configuration. Ideally, the batteries should be charged individually so that there is no electrical imbalance during the process.

Now, when you are doing the same with batteries that are connected in a parallel configuration, it might take longer to get the job done because their amp-hour capacity has been increased. This is, of course, when you are charging them in bulk.

Batteries are connected in a series configuration when they are required to power applications that need a higher voltage. But they are connected in a parallel configuration when they are required to have more amp-hour capacity.

But remember that this does not mean a stack of batteries in a parallel configuration can actually power an application that needs more output voltage than the battery’s standard. It just means that this circuit will be able to power the application that is meant for this output voltage for a longer period of time.

And note that the total energy is going to be the same no matter how you connect them. This is measured in watt-hours.

Now to the question of which one is better for you. That depends on the output you want.

Dealing with Series Configuration

When you connect a group of batteries in a series, you connect the positive terminal of the first battery with the negative of the second and so on in a sequence. It is quite literally a series and that’s why it is called so.

But after you do this, you must measure the total output voltage between the negative of the first battery and the positive of the last one. For instance, if you connect two 12-volt 100 amp-hour (Ah) batteries in a series configuration, you will see that the total voltage is 24 volts and the capacity remains at 100 amp-hours, as it should. If you keep adding batteries, you will notice an increase in the voltage but not in the capacity.

Let’s take an example to understand when the series configuration is a good idea. If you want to power a 360-watt application, you will need 12-volt batteries that draw 30 amps of power. This is calculated using the formula:

Power of the device (watts) = operating voltage (volts) x the current drawn (amps)

Now, if you had batteries powering it at 24 volts, the 360-watt application would draw only 15 amps. This is because the series configuration gives the overall system a higher output voltage. When it draws a lower system current, you will be able to use thinner wires and that will result in less drop in the voltage of the overall system.

Another scenario when the series configuration is good is if you have to control charge. A 50-amp charge controller can handle about 600W of power but if you have 24-volt batteries connected, it can 1,200 watts (24 volts x 50 amps). So if you want to operate large power systems, connecting the batteries in series is a good choice.

But this system isn’t without flaws. When you connect batteries in a series, you cannot reduce the voltage of the bank.

Dealing with Parallel Configuration

When you connect a group of batteries in a parallel configuration, you connect all the positive terminals to each other and do the same with the negative terminals too. This results in the circuit having the same output voltage but with an increase in amp-hours.

For example, if you connect two 12-volt, 100 Ah batteries in a parallel configuration, you will see that the total capacity of the circuit will be 200 Ah but the output voltage will hold steady at 12 volts. If you add another battery with the same voltage and capacity, you can increase the system capacity to 300 Ah while the output voltage will still be 12 volts.

This system is great when you want to increase the runtime of an electrical application without messing with its voltage. Doubling the number of batteries will power the application for twice the amount of time and the same logic applies for three batteries that are connected in a parallel configuration. In fact, if one of the batteries in the circuit dies, you can still power the application with the other two batteries.

The problem with this system is that since the output voltage is low compared to the capacity, the current draw will be higher. That means, you will need thicker wires and even then you will see an increase in voltage drop. This is very inefficient when working with large power applications at a lower voltage.

Frequently Asked Questions

What Does Batteries in Parallel Mean?

It means that multiple batteries are connected in a parallel configuration. This means the positive terminals of all the batteries are connected with one wire and the negative terminals of the same batteries are connected with another wire.

The open ends of both these wires are then connected to the electrical application that needs to be powered. When batteries are connected in this configuration, they gain more system capacity while the output voltage remains the same.

Do Batteries Last Longer in Series or Parallel?

Parallel. When you connect multiple batteries in a series configuration, only their voltage increases. But when you connect them in a parallel configuration, the overall system capacity is increased. This means that the amount of available current in the circuit is increased and the batteries can last longer. That is why this configuration is preferred when you need to increase the runtime of a certain application.

For instance, if you connect two 6-volt batteries in a parallel configuration, you can power a 6-volt device for double the duration.

About the author

Hi, I'm Phil Borges.. thanks for reading.. My wife says I can't shut up about batteries so to save my marriage I've started this blog .. where I'd be ranting about batteries! Please leave a comment if you have any questions, I'm happy to help!

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