How To Charge LiFePO4 Batteries in Parallel?

By Matthew Joseph Nandirio •  Updated: 10/22/22 •  6 min read

Whether you can charge your LiFePO4 battery in parallel is confusing since you will only find conflicting information online. 

That’s why I have decided to put an end to it and write about how you can charge your LiFePO4 battery in parallel. Let’s see how it works. 

Solar Inverter
Solar Inverter

How To Charge LiFePO4 Batteries In Parallel?

To charge LiFePO4 batteries in a parallel circuit, you have to connect the positive output of your charger to the positive terminal of your batteries and the negative output of the charger to the negative terminal of your batteries. 

According to a study published in the Applied Energy journal, some aspects of parallel charging exist.

  • You have to understand that when you connect two or more LiFePO4 batteries in parallel, the current will not necessarily pass equally through each one of them. 
  • This unequal current flow between LiFePO4 batteries is caused by differences in the battery connection, resistance, manufacturing variations, and even temperature. 
  • Because of the differences in current, each parallel branch causes the state of charge of your LiFePO4 battery to diverge. 
  • Since the discharge rate of the LiFePO4 battery is very slow, it will take hours to equalize the state of charge after removing a load. 

Charging LiFePO4 Battery in Parallel Circuit : Two Methods Explained

Charging the battery in a parallel circuit means you are not charging the voltage of your battery; instead, you are charging the amp-hour capacity. 

Parallel Connection Between Two Batteries
Parallel Connection Between Two Batteries

In a parallel connection, your battery will have an increased Ah capacity, but the voltage will remain the same across the battery. However, there are typically three methods of charging your LiFePO4 batteries in parallel. 

Method 1: Unbalanced Charging 

In this method, different sizes and ages of LiFePO4 batteries are connected in a parallel circuit, and it’s an unbalanced connection. In this formation, your battery pack will have an uneven resistance level. Thus, it can fail prematurely or have a shortened lifespan. 

Method 2: Balanced Charging

Balanced charging in parallel is a better method than the previous one. To achieve balanced charging, you have to start one of the charging leads from the opposite direction. The amperage drawn by your battery in this method looks symmetrical. 

You can use both even and odd numbers of strings. The difference between the primary and secondary contact batteries will not be more than 15%. 

Method 3: Perfectly Balanced Charging

In this configuration, you will need a similar length of wires throughout the entire system to maintain the same resistance level. Perfectly balanced charging in a parallel circuit will draw the same amount of current from the charger. 

Since your batteries will be charged and discharged evenly, their lifespan will automatically increase. But you can only achieve perfectly balanced charging when there are even numbers of batteries. 

Advantages & Disadvantages of Parallel Circuit for Charging LiFePO4 Battery

You will find many advantages as well as some disadvantages of parallel charging. Here are some advantages of charging your LiFePO4 battery in parallel. 

  • It will save you a lot of time. You can charge multiple battery pack charge at once. Plus, you just have to connect everything once. 
  • It can charge multiple battery packs more efficiently than series charging. 
  • As the voltage will remain the same, your charger must do less work. 
  • Ensures safer charging compared to the series circuit. As you can connect the battery pack in any order, the chances of mixing up and creating a direct short are very low. 

Now, here are some disadvantages of parallel charging for LiFePO4 batteries. 

  • If anything happens during the charge cycle, it will affect multiple battery packs, if not all. 
  • You cannot monitor each battery pack separately during charging. 
  • If you have huge differences in voltage between your battery packs, it can pass a huge amount of current between the packs, damaging the wiring. 
  • You cannot use less capable chargers with parallel connections. Only larger chargers are good for this circuit. 

If you wonder about the ins and outs of a series connection of LiFePO4 batteries to understand more, then refer to our mentioned article above.

A Step-By-Step Process to Charge LiFePO4 Battery in Parallel 

You now have a basic understanding of parallel charging, how it works, and why you should use it. So, now I’ll show you a detailed step-by-step process to charge your LiFePO4 battery in a parallel circuit. 

But before that, you must know what components you need for parallel charging. Here’s a list: 

  • A parallel wiring adapter for the main lead is based on your choice. 
  • A parallel wiring adapter for the balance lead. 
  • Your battery pack 
  • Wires 

Now that you know what equipment you will need, it’s time to show the parallel connection process. 

Here’s a step-by-step process of charging the LiFePO4 battery in a parallel circuit. 

Step 1: Determining the Method

Your parallel charging connection process starts with determining which type of parallel connection you want if you have LiFePO4 batteries of different sizes and ages. 

But you can have a balanced connection if you have the same sizes and ages of batteries in uneven numbers. And if you have an even number of LiFePO4 batteries, you will get a perfectly balanced parallel connection. 

Step 2: Connecting the Positive Terminals

The process is quite simple. Use one branch of a parallel circuit to charge each battery with a single charger. You have to connect your battery charger’s positive output to the first battery’s positive terminal. 

Then connect that positive terminal to the positive terminal of the second battery. Keep doing this until all your batteries are connected. 

Step 3: Connecting the Negative Terminals 

Now, connect the negative output of your charger to the negative end of your first battery. This way, connect all the negative ends of your battery as you did for the positive ones. 

Step 4: Checking & Testing 

This final stage is where you check and test your parallel charging system. See whether the main lead and balance lead wires are properly connected. 

Then check whether your battery is charging. This is how you will charge your LiFePO4 battery in a parallel circuit. 

Final Thoughts 

Charging your LiFePO4 battery in the parallel circuit can be a faster and less costly way. But make sure you use an even number of batteries that are in similar condition. That’s how you will get maximum benefits from it. 

References 

1. S. Wenji et al. (2019). Performance of LiFePO4 batteries in parallel based on connection topology. 

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Matthew Joseph Nandirio

Matthew Joseph Nandirio is the Founder of walkingsolar. After graduating from the University of Houston in 2002, matt started working as an electrical and electronic engineer for several multi-national solar energy companies. He has a wide range of experiences including solar system requirement analysis, planning, maintaining, debugging and even solar device development through research. He now shares his 20 years of expertise through his articles on the walkingsolar website. Further, he is also the author of two books on Solar Technology, “Solar Power for Villages” and “DIY Solar System for Dummies”.

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