Battery Bank Tutorial: Joining Batteries Via Series or Parallel for Increased Power
What is a battery bank? No, battery banks are not some financial battery establishments. A battery bank is a result of connecting two or more batteries together for a single application. 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, a deep cycle AGM or GEL cell battery in the group 24, group 27, group 31, or golf cart GC2 group size is much more affordable than purchasing a massively heavy group 4D or 8D battery for your RV, camper, trailer, or boat.
The first thing you need to know is that there are two primary ways to successfully connect two or more batteries: The first is via a series connection, and the second is called a parallel connection. Let’s start with the series method as we compare series vs. parallel.
How to wire batteries in series:
Connecting batteries in series adds the voltage of the two batteries, but it keeps the same AH rating (also known as Amp Hours). For example, these two 6-volt batteries are wired in series now produce 12 volts, but they still have a total capacity of 10 amps.
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 6 volts, but the amps increase to 20 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:
It is also possible to connect batteries in series and parallel. While this may sound confusing, it is not too hard, and we will walk you through the steps below. A series-parallel connection can increase your voltage output and the AH rating of the battery pack. To do this successfully, you need at least four batteries.
If you have two sets of batteries already connected in parallel, you can wire both sets into a series connection that will make a series-parallel battery bank. In the diagram above, we have a battery bank that produces 12 volts and has 20 amp hours.
Don't get lost now. Remember, electricity flows through a series connections like in a single battery. It can't tell the difference. Therefore, you can series two batteries that are in parallel with another set to create a series-parallel setup. For this type of setup, only one cable is needed to make the series connection which will bridge the positive terminal from one parallel bank to a negative terminal on the other.
Many customers often ask if they can put a set of batteries in series first and then parallel each set of batteries. Either way is ok, as electricity will flow through parallel or series connections the same way it would if you were only using two batteries. Many customers prefer to put their batteries in series first when using 6v batteries as 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 significaly 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.