Building a battery bank using amp hours batteries. Battery bank connection

Series vs. Parallel Connections Explained

While researching lithium batteries, you’ve probably seen the terms series and parallel mentioned. We are frequently asked the questions like, what’s the difference between series and parallel”, “can RELiON batteries be connected in series.” It can be confusing if you’re new to lithium batteries or batteries in general, but hopefully, we can help simplify it.

Let’s start at the beginning. your battery bank. The battery bank is the result of connecting two or more batteries together for a single application (i.e. a sailboat). What does joining more than one battery together accomplish? By connecting the batteries, you either increase the voltage or amp-hour capacity and sometimes both, ultimately allowing for more power and/or energy.

The first thing you need to know is there are two primary ways to successfully connect two or more batteries: The first is called a series connection and the second is called a parallel connection.

Series Connections

Series connections involve connecting 2 or more batteries together to increase the voltage of the battery system but keeps the same amp-hour rating. Keep in mind in series connections each battery needs to have the same voltage and capacity rating, or you can end up damaging the battery. To connect batteries in series, you connect the positive terminal of one battery to the negative of another until the desired voltage is achieved. When charging batteries in series, you need to utilize a charger that matches the system voltage. We recommend you charge each battery individually, with a multi-bank charger, to avoid an imbalance between batteries.

In the image below, there are two 12V batteries connected in series which turns this battery bank into a 24V system. You can also see that the bank still has a total capacity rating of 100 Ah.

Parallel Connections

Parallel connections involve connecting 2 or more batteries together to increase the amp-hour capacity of the battery bank, but your voltage stays the same. To connect batteries in parallel, the positive terminals are connected together via a cable and the negative terminals are connected together with another cable until you reach your desired capacity.

A parallel connection is not meant to allow your batteries to power anything above its standard voltage output, but rather increase the duration for which it could power equipment. It’s important to note that when charging batteries that are connected in parallel, the increased amp-hour capacity may require a longer charge time.

In the example below, we have two 12V batteries, but you see the amp-hours increase to 200 Ah.

Can RELiON Batteries Be Connected in Series or Parallel?

Our standard lithium batteries can be wired in either series or parallel based on what you’re trying to accomplish in your specific application. RELiON’s data sheets indicate the number of batteries that can be connected in series by model. We typically recommend a maximum of 4 batteries in parallel for our standard product, however, there may be exceptions that allow for more depending on your application.

When using RELiON’s lithium batteries, there are a few items to note, specific to our series:

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Our HP Series batteries can be connected in parallel only.

Our InSight batteries can only be connected in parallel and allows for up to 10 batteries in parallel.

Whether you’re seeking an increase in voltage or amp-hour capacity it’s important to understand the difference between parallel and series configurations, and the effects they have on your battery bank’s performance. Knowing the differences between these parallel versus series configurations allows you to maximize your lithium battery’s life and overall performance.

To learn more about how to calculate your energy needs and find the optimal battery for your application and usage, visit our Lithium Battery Selector Tool.

Have more questions?Visit our FAQs page for more commonly asked questions on lithium batteries.

Ready to purchase your next battery bank?Check out our full line of lithium batteries.

Building a battery bank using amp hours batteries

In this article we’ll look at different ways to build a battery bank (and ways not to) for amp hour rated batteries (and ways not to). In the illustrations we use sealed lead acid batteries but the concepts are true for all battery chemistries.

The battery bank cheat sheet for amp hour rated batteries

If you know your batteries and you’re just looking for a memory jogger here’s the battery bank cheat sheet. detailed explanations and tutorials are shown below.

What are battery banks and why have them?

A battery bank is simply a set of batteries connected together in a certain way to provide the needed power. Sometimes battery banks are the preferred choice compared to just buying one large battery for reasons such as:

  • Cost – a number of small batteries can be cheaper to purchase, especially if they are popular and so there are several manufacturers or suppliers to chose from.
  • Space – several small batteries can be arranged in awkward spaces where a large rectangular block wouldn’t fit.
  • Flexibility – you can rearrange the layout of a battery bank to give you different voltages and ampere hours rather than being stuck with one battery that has one voltage and one ampere hour output.

Building an amp hour battery bank

In this article we’ll show the different ways batteries can be wired together in order to get different capacities (voltage and amp hour outputs).

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In our example we’ll use several 6 volt 4.5 amp hour batteries as follows:

Number of Batteries Wiring Output
2 Connected in Parallel 6 volts, 9 Ah
2 Connected in Series 12 volts, 4.5 Ah
4 Connected in Parallel 6 volts, 18 Ah
4 Connected in Series 24 volts, 4.5 Ah
4 Connected in Parallel and Series 12 volts, 9 Ah

Connecting two amp hour batteries in parallel

To calculate the output when wiring in parallel add the Ah ratings together. In this case 4.5 Ah 4.5 Ah = 9 Ah. The voltage does not change. Note the way the appliance is connected. Many sources explaining parallel wiring suggest the following instead:

This will work but a greater load is placed on the battery closest to the appliance which means the batteries will not wear out evenly. This is especially true of deep cycle batteries which are meant to discharge and recharge on a regular basis.

Connecting four amp hour batteries in parallel

To calculate the output when wiring in parallel add the Ah ratings together. In this case 4.5 Ah 4.5 Ah 4.5 Ah 4.5 Ah = 18 Ah. The voltage does not change. Again, note the way the battery bank is wired to the appliance so that the load is shared evenly across all the batteries. Some source suggest the following:

This layout will work but places greater loads on the batteries closer to the appliance causing them to wear out faster, especially if they are deep cycle batteries meant to discharge and recharge regularly.

Connecting two amp hour batteries in series

When connected in series the amp hour output does not change but the voltage becomes the sum of the batteries. In this case the voltage is calculated as 6 volts 6 volts = 12 volts. The ampere hour rating is unchanged at 4.5 Ah.

Connecting four amp hour batteries in series

Again to calculate the output voltage its just a case of adding the voltages of all the individual batteries together. Here it would be 6 volt 6 volt 6 volt 6 volt = 24 volt. The amperage is the same as for one battery – 4.5 Ah

Connecting batteries in series and parallel

When you wire batteries together in parallel you are essentially just making each battery a cell of a larger unit. So you could, for example, arrange each pair wired in parallel and then wire the two pairs together in series as follows:

To calculate the output we have:

  • Two pairs connected in parallel. Each pair has an amp hour output of 4.5 Ah 4.5 Ah = 9 Ah but because they are wired in parallel their voltage is unchanged at 6 volts.
  • The pairs are then wired in series so the voltage is the sum of each pair: 6 volts 6 volts = 12 volts.
  • Altogether then this creates a battery bank with an output of 9Ah and 12 volts.

You can continue to scale this up as needed. All you have to remember is that each set of batteries connected in parallel gives the same output.

Connections and wiring

To achieve the expected results with a battery bank and stay safe ensure the following:

  • Use the correct connectors which will be defined by the battery terminal (see [link to battery terminal types ] article). Make sure if you need to connect two wires to one terminal you have a connector designed to take two wires. Although clips can be used temporarily they are not recommended as they do not always provide solid connection and they could easily come loose raising the risk of short circuits which would damage the batteries and could cause electric shocks.
  • Use the correct gauge of wiring for the circuit you are creating (see [link to wiring calculator] ). If the wire is too thin it could overheat raising the risk of short circuits, electric shocks, battery damage or even fire.

Battery banks with different amp hour or voltage ratings

So far the examples all used identical batteries but what if you have different batteries that you want to wire together?

  • Connecting batteries with different voltages in series – on paper this is possible but in reality slightly batteries with different voltages often have slightly different cell voltages and the same is true of ampere ratings. The result is smaller batteries will over-discharge and overcharge while larger batteries will not fully recharge. In exceptional circumstances an over-discharged battery may leak or explode. For full details see Connecting batteries in series.
  • Connecting batteries with different ampere ratings in series – as with different voltages smaller ampere rated batteries will drain faster and deeper than they are designed to withstand. For details on this process and why it occurs see Connecting batteries in series.
  • Connecting batteries with different voltages in parallel – this is a “never, never” idea. The larger rated battery will attempt to charge the smaller leading to battery damage in the best case scenario or fires and explosions in extreme situations where voltages are substantially different or primary (disposable) batteries are in use. For more on this see Connecting batteries in parallel.
  • Connecting batteries with different ampere ratings in parallel – this is possible but again the reality is that batteries with different ampere ratings usually have different cell voltages (no matter what the label actually says) which can lead to problems as batteries try to charge each other and balance out voltages across the circuit. See Connecting batteries in parallel for full details.

As an example the layout pictured is theoretically correct because on paper each row has an output of 9Ah and 6 volts. However small differences in the manufacturing process between the two models can cause issues.

Lets say the two larger 6 volt batteries are truly 6 volts but the three smaller 6 volt batteries are each actually 6.2 volts despite what is written on the label. Here we’ll end up with the larger batteries over charging and discharging which will shorten their lifespan.

It will work, but this battery bank won’t last as long as one made up of identical batteries.

The role of age and chemistry in voltage and ampere capacity

It should always be borne in mind that age and chemistry affect the voltage and ampere capacity of batteries, both disposable and rechargeable.

Age – All disposable batteries self discharge and all rechargeable ones slowly loose their ability to fully recharge as they get older. As such even if you have batteries of the same make and brand, if one is significantly older than the others this is the same as mixing batteries of different voltage and ampere capacity

Chemistry – Even batteries closely related (such as sealed lead acid batteries and flooded lead acid batteries) behave differently in the way they charge and discharge so it is important to ensure that all units in a battery bank are of the same chemistry in order to avoid some units over-discharging and overcharging.

Battery bank best practices

As discussed above building battery banks using different batteries with different voltages and ampere hour ratings can damage the batteries and in extreme circumstances lead to explosions or fires. Even batteries of identical voltage and ampere hour ratings can cause damage if old and new units are mixed. These issues can only be avoided with the correct tools and circuitry. Without these it is better practice to use:

  • batteries of the same voltage and ampere hour rating
  • batteries of the same age and chemistry type
  • ideally batteries of the same brand from the same company and if possible from the same production run

… and when you have an issue with the battery bank because of one faulty battery replace all the batteries, not just the faulty one.

Maximum size of a battery bank

There isn’t really any maximum. Some battery banks are huge like the one pictured here which is designed to store energy from solar panels.

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In this type of application the battery bank needs to store vast amounts of energy and its a clear example of where many smaller batteries connected together is far more practical than large batteries.

Damaged or worn out units can be replaced easily and the size of the battery bank and be increased or decreased by small amounts as needed.

To imagine this lets say each long row of batteries in the room have an output of 240 volts and 500 amp hours and there are three rows connected in parallel so the total output of the battery bank is 240 volts and 1,500 amp hours (500 Ah x 3 rows).

The engineers decide they actually now need 2,000 amp hours so all they need to do is add another identical row wired in parallel to achieve their goal.

The replace one or replace all argument

Now you may have noticed there seems to be a contradiction above. Earlier we mentioned that if one battery fails in your battery bank then you should replace all the units but when we talk about very large battery banks we say this practice is not always followed.

The decision is more accurately based on a number of factors to balance cost and lifespan:

  • SCENARIO 1: If a battery bank if fairly new (say 6 months old) and one battery fails that failure is probably down to a manufacturing fault. In this case sourcing a new battery (ideally from the same manufacturer) to replace that single unit would be the best approach, especially if the battery bank is extremely large.
  • SCENARIO 2: If a battery bank if coming to the end of its lifespan then replacing each single unit as it fails will quickly damage these new batteries and shorten their lifespan leading to a constant vicious cycle of replacements that would not be economical in the medium or long term. As such in this situation all batteries in the bank should be replaced.
  • SCENARIO 3: If a battery bank is mid way through its lifespan and one unit fails then it is possible to replace it with a new unit provided the battery bank is fitted with the correct circuitry to balance charging and discharging to the new unit. The costs of such circuitry makes economic sense in large scale commercial battery banks.

How to Connect Charge Batteries in Series / Parallel

If you want to know about charging batteries in series and parallel then you have probably asked or are wondering what the advantage is of connecting batteries in series / parallel. This tutorial will provide easy to understand diagrams and will share reasons why you would use this battery configuration.

If you need to know about charging parallel batteries then click over to our tutorial on perfectly balanced charging. You may discover why your batteries have not been lasting as long as you thought they should!

Before we dive in any further, we would like to pause and thank our friends over at Iota Engineering for creating the graphics. Iota manufactures the very popular DLS line of power supply chargers found in many of our customers fifth wheels, RVs, and telecommunications applications. The charger depicted in some of the images will resemble their DLS charger and will have their logo emblazed on it.

Batteries Connected in Series

When connecting or charging batteries in series your goal is to increase the output of your batteries nominal voltage rating. To do this you need to connect the POS terminal of the first battery to the NEG (-) terminal of the second battery. If there are only two batteries in our series we would then take a wire from the NEG (-) terminal of the first battery and a wire from the POS of the second battery to the motor or charger.

The positive of the first battery and negative of the second battery DO NOT connect to each other! The series configuration DOES NOT increase your amp hour capacity; it only increases your voltage output.

If you need to connect more than two batteries in series, you would make the following adjustment. Instead of connecting the POS of the second battery to the charger, you would connect it to the NEG (-) of the third battery. You would continue this positive to negative pattern until you reach your last battery. The POS of the last battery in the series will connect to your application / charger.

For most of our customers, 6-volt batteries will be used in their series/parallel configuration. The images used here will FOCUS on this setup, but if you are using 12-volt batteries simply swap the numbers; the connections will be the same.

Series / Parallel Combination

The goal of the series / parallel configuration is to increase BOTH the voltage and capacity. Batteries that are ONLY in parallel keep the same voltage and increase their capacity. Batteries that are ONLY in series keep the same capacity and increase their voltage. Combining the two provides the best of both worlds; increasing Both voltage and amperage.

The series parallel combination can look confusing when you first come across a jumble of wires atop your battery bank. Hopefully this diagram will simplify what you are seeing.

As you can see, we now have a LEFT battery bank and a RIGHT battery bank (the dotted line around each). The left bank has an extra black wire connected to the NEG (-) terminal of battery number one. This wire attaches to the NEG (-) terminal of the corresponding battery bank to the right (battery number three if we keep our numbering sequence).

The same pattern can be seen with the positive terminals. The right battery bank has an extra red wire on the POS terminal of battery number four. This wire connects back to the POS terminal of battery number two in the left bank.

The extra red and black wires are what tie the system together in parallel. They are what allow the system to increase, in this case double, the amp hour capacity. If you are adding more battery banks to increase capacity even further, simply push the charger off to the right and follow the pattern already established with the NEG (-) to NEG (-) black wire and the POS to POS red wires.

A Battery Word Equation and Special Note


B1 POS to B2 POS and B1 NEG (-) to B2 NEG (-)

Battery Capacity x Number of Batteries = Battery Bank Capacity


B1 POS to B2 NEG (-) with B1 NEG (-) and B2 POS to Application

Voltage of Battery x Number of Batteries = Battery Bank Voltage


Battery Bank Voltage (Battery Capacity x Battery Banks) = System Capacity and Voltage

Note: that for optimal battery bank and charging performance, the batteries in the bank should be of the same manufacturer and model, as well as the same AH rating, age, condition, and state of charge [SOC].

One major reason for utilizing the series parallel combination is simply due to space restrictions and the need to maximize capacity storage. Sometimes you can gain higher amperage in a different or smaller footprint using 6V batteries rather than 12V batteries.

There are many that grew up with the idea that the longevity of 6V batteries with their thicker plates will far outweigh that of 12-volt deep cycle batteries. To gain this extra durability they prefer to use only 6-volt batteries and thus need to create a series parallel configuration.

Hopefully this tutorial bridged the gap in your understanding series connections and will provide you the confidence needed help connect and charge your batteries in series and parallel.

Great job. This was very well explained and drawn out. Question, does it matter that the charging red start at battery 4 versus battery 2? Since they are connected is there a difference as to which battery bank received the direct charging connection? Same with the negative connection? Thanks.

Very usefull, but is tyhere a way so i can power a circuit with batteries in a parallel configuration, but charge them using a series configuration? May be using diodes?

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How to wire 6V Batteries in series or parallel configuration

How do you create a multi-bank battery system for an RV, boat or other application? It’s rather simple but it requires you to know how to wire 6V batteries in series or parallel configuration.

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There are several reasons why you may want to configure multiple batteries together; whether it be for cost savings, efficiency or increasing voltage or capacity. There are basically two ways to configure multiple battery systems, in Series or in Parallel. There is also a Series/Parallel combination as well. This article will help you to wire 6 volt batteries.

Wiring Batteries in a Series

In a Series Configuration the batteries are wired per the diagram below and the result would be a doubling of the voltage while the capacity remains the same. In our illustration we show two 6V batteries with 225AH wired together. The result would be a battery bank that produces 12V and 225AH.

Wiring Batteries in Parallel

In a Parallel Configuration the batteries are wired per the diagram below and the result would be a doubling of the capacity while the voltage remains the same. In our illustration we show two 6V batteries with 225AH wired together. The result would be a battery bank that produces 6V and 450AH.

Wiring Batteries in Series/Parallel Combination

In a Series/Parallel Combo Configuration the batteries are wired per the diagram below and the result would be a doubling of the voltage and doubling of the capacity. In our illustration we show four (4) 6V batteries with 225AH wired together. Each set is wired in series creating 2 banks, then the 2 banks are wired together in a parallel configuration. The result would be a battery bank that produces 12V and 450AH.

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