How To Connect Batteries In Series and Parallel

What is a battery bank? No, battery banks are not some financial battery establishments. A battery bank is connecting two or more batteries together for a single application. You might ask, what does this accomplish? By linking batteries together, you can increase the voltage, capacity (AH / Wh), or both.

When you need more power, you can construct a battery bank using widely available batteries. For instance, using a common group-size battery such as a group  24, group 27, group 31, or golf cart GC2 group size is much more affordable than purchasing a heavy group 4D or 8D battery for your RV, camper, trailer, or boat.

The first thing you need to know is that there are three primary ways to successfully connect batteries: The first is via a series connection, the second is called a parallel connection, and the third option is a combination of the two called a series-parallel connection.

How to wire batteries in series:

Connecting batteries in series increases the voltage of a battery pack, but the AH rating (also known as Amp Hours) remains the same. For example, these two 12-volt batteries are wired in series and now produce 24 volts, but they still have a total capacity of 35 AH.

To connect batteries in a series, use a jumper wire to connect the first battery's negative terminal to the second battery's positive terminal. This leaves you a positive terminal on the first battery and a negative one on the second battery to use for your application.

When connecting batteries: Never cross the remaining open positive and negative terminals with each other, as this will short-circuit the batteries and cause damage or injury.

Be sure the batteries you're connecting have the same voltage and capacity rating and are of the same batch. Otherwise, you may end up with charging problems and shortened battery life.

How to wire batteries in parallel:

The other type of connection is parallel. Parallel connections will increase your capacity rating, but the voltage will stay the same. In the “Parallel” diagram, we're back to 12 volts, but the amps increase to 70 AH. It's important to note that if you plan on pulling more amperage than the system was designed for, you may need to upgrade to a heavier-duty cable to keep the wires from burning up.

To join batteries in parallel, use a jumper wire to connect positive terminals together, and another jumper wire to connect negative terminals together. This establishes negatives to negatives and positives to positives. You CAN connect your load to ONE of the batteries, which will drain both equally. However, the preferred method for keeping the batteries equalized is connecting to the positive at one end of the battery pack and the negative at the other end.

How to wire in a series-parallel configuration:

If you have two sets of batteries connected in series, you can wire both sets into a parallel connection to make a series-parallel battery bank. In the images below we will walk you through the steps to create a 24 volts 70 AH battery pack.

Don't get lost now. Remember, electricity flows through parallel or series connections as if it were a single battery. It can't tell the difference.

Therefore, you can parallel two sets of batteries that are in series to create a series-parallel setup.

Creating a series-parallel battery bank:

Step 1 - Series First

First, we recommend putting each set in series first. To do this, you will use a jumper between the inner positive and negative terminals of each set to increase the voltage, as seen in the picture below:

Step 2 - Parallel Each Series Set:

Once each set has been put in series, you can use jumpers to parallel each set together. Basically, the outer positives to positives and outer negatives to negatives, as seen in the final picture below:

Many customers ask if they can put a set of batteries in parallel first and then in series. Either way is okay, as electricity will flow through parallel or series connections like it would if you were only using two batteries.

In other words, there is no right or wrong method. However, most customers prefer to put their batteries in series first because it allows them to use onboard desulfators more effectively to extend battery life.

Don’t be concerned if a terminal has more than one cable connected to it. It's necessary to construct these kinds of battery banks successfully.

In theory, you can connect as many batteries as you want. But when you start constructing a tangled mess of batteries and cables, it can be very confusing, and confusion can be dangerous. Keep in mind the requirements for your application, and stick to them. Also, use batteries of the same capabilities. Avoid mixing and matching battery sizes wherever possible.

Always remember to be safe and keep track of your connections. If it helps, make a diagram of your battery banks before attempting to construct them. Good luck!

Quick Vocabulary Reference:

AMP Hour is a unit of measure for a battery's electrical storage capacity. A manufacturer will subject the battery to a specific amp draw over a 20 hour timeframe in order to determine the AH capacity. The amp/hr rating can significantly change based on the given load applied for more information see our article: Peukert’s Law | A Nerd’s Attempt to Explain Battery Capacity.

Voltage represents the pressure of electricity. Some applications require more "pressure," meaning higher voltage.

Choose a More Powerful Battery

If you have ever worked with batteries you have probably come across the terms series, parallel, and series-parallel, but what exactly do these terms mean?

Series, Series-Parallel, and Parallel is the act of connecting two batteries together, but why would you want to connect two or more batteries together in the first place?

By connecting two or more batteries in either series, series-parallel, or parallel, you can increase the voltage or amp-hour capacity, or even both; allowing for higher voltage applications or power hungry applications.

CONNECTING BATTERIES IN SERIES

Connecting a battery in series is when you connect two or more batteries together to increase the battery systems overall voltage, connecting batteries in series does not increase the capacity only the voltage.
For example if you connect four 12Volt 26Ah batteries you will have a battery voltage of 48Volts and battery capacity of 26Ah.

To configure batteries with a series connection each battery must have the same voltage and capacity rating, or you can potentially damage the batteries. For example you can connect two 6Volt 10Ah batteries together in series but you cannot connect one 6V 10Ah battery with one 12V 20Ah battery.

To connect a group of batteries in series you connect the negative terminal of one battery to the positive terminal of another and so on until all batteries are connected. You would then connect a link/cable to the negative terminal of the first battery in your string of batteries to your application, then another cable to the positive terminal of the last battery in your string to your application.

When charging batteries in series, you need to use a charger that matches the battery system voltage. We recommend you charge each battery individually to avoid battery imbalance.

Sealed lead acid batteries have been the battery of choice for long string, high voltage battery systems for many years, although lithium batteries can be configured in series, it requires attention to the BMS or PCM.

CONNECTING BATTERIES IN PARALLEL

Connecting a battery in parallel is when you connect two or more batteries together to increase the amp-hour capacity. With a parallel battery connection the capacity will increase, however the battery voltage will remain the same.

Batteries connected in parallel must be of the same voltage, i.e. a 12V battery can not be connected in parallel with a 6V battery. It is best to also use batteries of the same capacity when using parallel connections.

For example, if you connect four 12V 100Ah batteries in parallel, you would get a 12V 400Ah battery system.

When connecting batteries in parallel, the negative terminal of one battery is connected to the negative terminal of the next and so on through the string of batteries. The same is done with positive terminals, i.e. the positive terminal of one battery to the positive terminal of the next.

For example, let’s say you needed a 12V 300Ah battery system. You will need to connect three 12V 100Ah batteries together in parallel.

Parallel battery configuration helps increase the duration in which batteries can power equipment, but due to the increased amp-hour capacity they can take longer to charge than series connected batteries. This time can safely be reduced, without damaging the batteries, by charging faster. Now that the battery is larger, a higher current charge is still the same percentage of the total capacity, and each battery ‘feels’ a smaller current.

While it is often debated what the best way to connect in parallel is, the above method is common for low current applications. For high current applications, talk to one of our experts as your situation may need a special configuration to ensure all of the batteries age at as similar as possible rates.

SERIES – PARALLEL CONNECTED BATTERIES

Last but not least! There is series-parallel connected batteries. Series-parallel connection is when you connect a string of batteries to increase both the voltage and capacity of the battery system.

For example, you can connect six 6V 100Ah batteries together to give you a 12V 300Ah battery, this is achieved by configuring three strings of two batteries.

In this connection you will have two or more sets of batteries which will be configured in both series and parallel to increase the system capacity.

If you need any help with configuring batteries in series, parallel or series parallel please get in contact with one of our battery experts.