LiFePO4 (Lithium Iron Phosphate) batteries are used widely for energy storage or backup. And it's no wonder. Afterall, they are safe, have stable chemistry and they last long. 

But sometimes, you may need to combine several batteries together to get the most of your setup. You may either connect in series or parallel, depending on your need. In this guide, we will walk you through the different connection types. Also, you'll understand the pros and cons of each method. 

How to Connect LiFePO4 Batteries Safely

Sometimes, you want to increase the system voltage or extend runtime. They each require a different type of connection. Also, how you wire your batteries directly affects performance, efficiency, and safety.

There are two main connection types: parallel and series. We’d explain how you can safely wire your batteries in either connection type. First, let's see why safety matters. 

Why Safe Battery Connection Matters

A poor or unsafe connection can cause all sorts of problems that you'd rather avoid. For example, the battery lifespan can be reduced, due to imbalance or overheating. Also, battery performance will be affected. Lastly, such poor connections can cause a fire and even damage your home or appliances. 

This is very different from the safety and peace of mind that you enjoy when the connection is proper. This is why it is important to connect batteries correctly. 

Reasons Why LiFePO4 Batteries Are Connected in Parallel or Series

Due to their design, you can combine LiFePO4 batteries to meet your specific energy needs. Often, people make this connection to: 

1. To Increase Capacity (Parallel Connection)

2. To Increase Voltage (Series Connection)

To Increase Capacity (Parallel Connection)

When batteries are connected in parallel, the voltage stays the same, but the capacities (Ah) are added. For example: Two 12V 100Ah batteries in parallel  is a 12V 200Ah system. 

This setup will last longer. This will allow your devices to stay on for longer before the battery drains. This connection is perfect when your equipment runs on 12V but you need longer battery life. Sometimes,you may notice this setup in homes or businesses that need a backup power. The setup is also common on RVs and mobile workshops. 

To Increase Voltage (Series Connection)

When batteries are connected in series, their voltages (V) add up while the capacity (Ah) stays the same. For example: Two 12V 100Ah batteries connected in series is equal to a 24V 100Ah system. 

This is ideal when your equipment or inverter needs a higher voltage to work well. Higher voltage also means lower current. This benefit will reduce heat and owners use thinner cables for the connection. This connection is common in solar energy systems with 24V or 48V inverters. Also, you may notice it in off-grid homes, to power high-load applications like water pumps.

What to Do Before Connecting Your Battery

Before connecting LiFePO4 batteries in series or parallel, there are a few things to note. Taking time to prepare your batteries will allow for a smooth setup and long-lasting system. Do not skip these steps as it could lead to poor performance, battery damage, and even hazards.

Ensure Batteries Are of the Same Brand, Voltage, and Capacity

To maintain battery balance and safety, all batteries in a bank should be uniform. Ensure they are the same:

• Brand (the same batch, if possible)

• Voltage (V) and capacity (Ah)

Mixing different batteries will cause charging and discharging issues. For example, it will stress the batteries and shorten their lifespan. But using similar batteries helps you avoid such a situation. 

Match Age, Charge Level (State of Charge), and Internal Resistance

Even when the batteries are similar, they should also have the same age and condition:

• Purchase the batteries around the same time

• The state of charge (SOC) should match 

You can measure each battery with a multimeter to ensure the voltage difference is no more than 0.05V. Similarly, the internal resistance should be close. A huge gap can cause one battery to overwork or be ineffective. These steps help avoid imbalance, which can be terrible in series connections.

Balance the Batteries

Before connecting batteries in series, they should be balanced, or their voltages should be equal. You can do this by:

1. Fully charge all batteries individually with the same charger

2. Allow the batteries rest for a few hours and check that their resting voltages are similar

These steps ensure that the batteries charge and discharge evenly. It prevents one battery from reaching empty or full before the others. Such a situation can cause battery degradation.

Use a Battery Management System (BMS) and Fuses

A Battery Management System (BMS) is quite essential. It will protect from overcharging, deep discharge, and overheating. Also, it monitors each battery's health and voltage. Alternatively, you can purchase Goldenmate's batteries with built-in BMS. 

Use Safety Gear

Before starting any wiring, wear insulated gloves and safety glasses. Also, use insulated tools to avoid accidental shorts. Remember to work in a dry, airy area. LiFePO4 batteries are safe, but some caution is always in place. 

Understanding Battery Connection Methods

Below, we explain the different connection methods. 

Parallel Connection of LiFePO4 Batteries

Parallel battery connection is one of the most common methods for expanding energy storage capacity. Use this setup when your devices or inverter operate at a fixed voltage (like 12V), but you need a longer runtime.

With parallel connection, you are joining all the positive terminals together and all the negative terminals together. Thus, the voltage remains the same but Amp-hour (Ah) capacity increases. Also, total energy stored (Wh) increases.

How to Connect in Parallel (Step-by-Step):

1. Keep the batteries identical and balanced.

2. Use thick, equal-length cables to reduce resistance.

3. Connect the positive (+) terminals of all batteries together.

4. Connect the negative (–) terminals of all batteries together.

5. Connect the load/inverter to the positive terminal of one battery and the negative terminal of the opposite end. This step helps distribute current evenly. It is known as diagonal wiring or cross-connection.

6. Add a main fuse or circuit breaker for system protection.

Pros

Increased Runtime: More amp-hours equals longer use hours. 

Increased Reliability: If one battery becomes weak or disconnected, the rest can still work. But the capacity of the system is affected. 

Easy to Scale: You can easily expand capacity by adding more batteries without affecting system voltage.

No Need to Change Equipment: If your devices or inverter are rated for 12V (or 24V), you can increase energy without changing your system voltage.

Cons

Risk of Imbalance: Different charge levels or internal resistance can cause some batteries to carry more load than others. The battery will wear faster as a result. 

Heavier Installation Cables: Because more current flows at lower voltage, you will need thicker wires and fuses. This setup causes heat and reduces efficiency.

Complex Wiring: Wiring can get complex with 3 or more batteries.

Series Connection of LiFePO4 Batteries

A series connection is used to increase the battery system voltage. Many solar inverters and off-grid applications may need this. Series wiring boosts voltage but keeps the battery capacity (Ah) the same. Here, the positive terminal of one battery is connected to the negative terminal of the next. 

This creates more total power (Wh) due to increased voltage. For example, two 12V 100Ah LiFePO4 batteries in series equal 24V 100Ah. Total energy = 24V × 100Ah (2400Wh). 

How to Connect in Series (Step-by-Step)

1. Confirm the batteries are balanced.

2. Connect the positive terminal of Battery A to the negative terminal of Battery B.

3. For more batteries (e.g., 3 or 4 in series), repeat the pattern: positive to negative.

4. The free negative terminal of the first battery and the free positive terminal of the last battery are your main output.

5. Add a BMS rated for the total system voltage and a fuse or circuit breaker at the output.

6. Use proper labeling and insulation to avoid confusion or shorts.

Remember, never connect batteries in series if their voltages are different.  This will cause charging issues and permanent damage.

Pros

Better Efficiency: Increasing system voltage will reduce energy losses in wiring. This efficiency may be helpful for high-power equipment.

Thinner Wiring: The system efficiency allows you to use thinner wires. This can save installation costs and space. 

Great for Large Inverters and High-Demand Systems: The connection will support systems that use a lot of power. 

Better for Long-Distance Connection: Higher voltage systems handle long cable runs better with less voltage drop.

Cons

Imbalance Risk is Higher: When one battery becomes weaker, the entire system is affected. Without a BMS or active balancer, this can cause over-discharge or overcharge.

Failure Affects the Whole Bank: If one battery fails, the entire connection may stop working until it is repaired.

More Dangerous Without Protection: Higher voltage systems need greater caution. Short circuits or reverse polarity can cause serious damage or fire. Use fuses, BMS, and insulated tools for safety.

How Many Batteries Can You Wire in Parallel or Series?

There are safe limits to how many batteries you can connect in series or parallel. These limits help maintain performance. Most manufacturers state how many batteries can be safely combined in either connection. For example, the Goldenmate 12V 100Ah LiFePO4 battery is rated 4P4S max. This means the limits for both parallel (P) and series (S) connections are 4 batteries.

How to Maintain Connected Batteries

Good maintenance will help your LiFePO4 battery bank last longer and perform better. Follow these easy steps:

• Check voltages regularly to ensure they're similar. 

• Keep connections clean and tight.

• Use a battery balancer or BMS to balance your batteries.

• Avoid Deep Discharges. Try not to drain batteries below 20% state of charge. 

• Use a compatible LiFePO4 charger.

• Keep batteries in an aerated and cool space.

• Replace faulty batteries promptly. 

Final Thought

Series and parallel connections of LiFePO₄ batteries allow you to scale your energy storage system based on your power and capacity needs. In series, the total voltage increases. Meanwhile, parallel connection increases the total capacity (Ah). 

We touched on the pros and cons of each connection. Remember to choose a connection based on your needs. Are you planning to scale your energy system/ Remember to order high-quality batteries from Goldenmate.