LiPo Battery Parallel Charging Tutorial

Parallel charging allows you to charge multiple LiPo batteries at once using a single charger. Parallel charging is also a more effective and faster way of charging your batteries.

Article first created in Dec 2014, last updated in Oct 2016.

Why Parallel Charging LiPo Batteries

Charging your batteries in parallel is nearly always faster than charging them individually. Even if your charger was not powerful enough to provide high current, parallel charging saves you from hooking/unhooking them up every charge cycle.

Apart from time saving, there is also benefit to the LiPo batteries and charger. The way I see it is, every battery has internal resistance, and the charger has to work hard to “pump” electricity into the battery. When you connect batteries in parallel, the total internal resistance is reduced, and the batteries becomes easier to charge (this is the Omh’s Law. For example, if you connect two identical resistors in parallel, the total resistance becomes half).

Furthermore, some decent para boards equipped with fuses which mean they might cut off the connection if there is a problem, to minimize the risk of damaging your battery or causing a fire.

parallel-charging-lipo-battery-power-quadcopter

Before You Parallel Charge, Read This

So parallel charging is an awesome way of charging your LiPo, but it’s also an advanced technique that requires some basic understanding of electricity.

Here are a few basic concepts and requirement that you need to understand first.

Cell Number – Your batteries have to be the same cell count number. You can only charge 2S battery with 2S batteries, and 3S with 3S and so on.

Capacity and C-Rating – Batteries connected in parallel may be of different capacities, but within reasonable range. For example 1000mAh pack can mix with 1500mAh. They can also be different C Rating (Lipo batteries can be charged at 1C safely)

Discharge State – The batteries should be at similar voltage level to be safe, but they don’t have to be at the exact same voltage, some tiny differences are allowed. Many people consider the difference within 0.1V is acceptable. The voltage difference will be neutralized when you plug them in. If the voltage difference is large, it would cause a very large current going between packs and could possibly burn your parallel board, the wires on the battery, or even the lipo itself.

Charge Current – When charging a single LiPo pack, I usually just charge them at 1C, which means the charge current = 1C * capacity. For example, for an 1800mAh pack, I charge it at 1.8A; and for an 800mAh pack, I use 0.8A. Of course you can choose to charge at higher C if your batteries allow.

The same principle applies when I charge multiple LiPo, the only difference is that the capacity is now the sum of all batteries connected. For example if I have 3 x 3S 2200mah batteries, the total capacity is now 6600mAh, and I can charge them at 6.6A.

How to Parallel Charge LiPo Safely

After you’ve understood what the requirements are for parallel charging, let’s talk about how to do it.

Getting a Para-Board

Firstly you will need get a parallel charging board (para-board) or adapter. Normally parallel charging boards have enough slots for 4 to 6 batteries. Each battery has one discharge lead (main plug), and one balance plug. You need to insert both connectors when parallel charging.

parallel-charging-board-adapter-lipo-battery

What I usually do is, I plug 2 or 3 batteries on each side, and put them into two separate LiPo Safe bags (3 packs each bag). They help reduce the risk of fire, although LiPo burns up in flame while charging is very uncommon. I have been using LiPo for over 5 years now and have never had a single fire incidence during charging. Anyway, better safe than sorry, right?

Depends on what kind of discharge leads your batteries have, you need to make sure they match the ones on the board (The ones in the picture are XT60 plug). If your batteries have a mix of different types of connectors (e.g. JST, T-connector), you could also get adapters for them instead of getting a whole new board.

Calculate Max Charging Current

Nowadays, smart chargers can automatically adjust charging current for you, depends on the maximum charging power it’s allowed and battery voltage. However if your charger doesn’t have this feature, you might want to manually calculate what the safe charging current limit is.

Assuming that I was using the Turnigy Accucel-6 charger (rated at 50 W) and I have 3 x 1300 mAh 3S LiPo batteries.

And I wanted to charge my batteries at 1C, which is 3.9A total charge current.

Charge current can be calculated by dividing power by voltage, I = P/V. But as you can see, voltage is changing all the time as the batteries get charged up, so will the current.

The voltage of each cell can reach as high as 4.2V during the charge cycle, which is 12.6V for a 3S pack.

The max power required is going to be: 12.6V * 3.9A = 49.14W. And Luckily, our charger is rated at 50W, so it meets our requirement, all good :)

However, what happens if I had four 1300 mAh 3S batteries, can I still charge at 1C?

1.3 A * 4 = 5.2 A
5.2 A * 12.6 V = 65.52 W

As you can see, I cannot charge 4 batteries at 1C in this case, as it will exceed the power limit of the charger.

Odds are, the charger might over heat and blow up if I insisted and set it to charge at 5.2A. To avoid burning my house down, I would have to select a lower charging rate: 50 W / 12.6 V = 3.968 A.

In reality, most smart chargers these days can automatically calculate this  for you (including the Accucel-6), and will set a upper bound limit to the charger’s current. Even if you set it to a higher value, it won’t go above that limit. Therefore I would recommend everyone to get a charger that comes with this feature, it’s just so much safer and easier!

I am currently using the iSDT SC620 charger, and absolutely love it! (04/Oct/2016)

Tips on Plugging in Batteries to Para-Board

Remember to always connect the discharge leads first, and then the balance leads. Because when you first connect the batteries together, the difference in voltage will cause a large current flow before they are equalized. The balance leads are much thinner and it could get damaged more easily, as they don’t take as much current as the discharge leads. It could even melt the traces on the parallel charging board like this.

para-board-trace-melt

Before you start parallel charging, make sure you do your research, read up and understand how to do this correctly.

The Science Behind Parallel Charging

So when all the lipo batteries are connected to the parallel charging board, they will be charged up and balanced nicely. You might wonder how it works though.

parallel-charging-connection-diagram-battery-charger

When they are connected in parallel, their voltages will become the same. As we mentioned earlier, the moment you connect them, there is a surge of current flow to equalize the voltage differences. They have now literally become a “huge single lipo battery”, with capacity combined. So basically we are just charging up one big lipo pack instead of smaller, separate packs in a sense.

But how does cell balancing work during charging? Similar to the above, the cells are also connected in each battery with the balance leads, for example cell1 in battery1 is connected with cell1 in battery2. These cells will also have their voltages “evened out”, again it acts like a single lipo pack.

That’s it!

It’s not unheard of that LiPo catch fire while charging. It could get quite dangerous especially when you have multiple batteries sitting next to each other. If you decide to go ahead with this, you do so at your own risk. If you are feeling uncomfortable or unsure, simply do not attempt it. Hopefully this short guide gave you some insight into what parallel charging is, and how to do it safely.

17 thoughts on “LiPo Battery Parallel Charging Tutorial

  1. Pavan Shetty

    Hi, I have a question regarding discharge of parallel connected LiPo batteries. I am connecting 2 6S LiPo batteries on my quadcopter. Since the batteries are connected in parallel will they try to charge each other? Thanks

    Reply
  2. Punkie

    I regularly parrallel charge, have for years and for the most part the packs come up fine. I’m worried today however.. I didn’t realize that on my last fly one of my packs got damaged, during the charge the voltage on one cell stayed around 3.7 while all the other cells were 4.1 when I noticed. I disconnected the faulty pack, re-balanced the other packs to storage levels and then charged them to full. After this I put each one on a discharge cycle individually and on each one the cell which had the low voltage dropped voltage to 4.09 immediately while the other cells were around 4.18. I’m currently balancing them again and hoping I haven’t permanently damaged all of those batteries. My fault if I have, I should be checking all batteries before charging..

    Reply
  3. Mr1337

    One question to all experts:
    fact ist:
    if you plug a SINGLE lipo to your charger and for example one of the balancer leads is damaged or you just forget to plug the balancer lead in your charger. Your charger would scream that something is wrong with the balancer plug. right?

    ok, now imagine you parall charge several lipos and you plug the lipo with the damaged balancer lead/plug.
    What would your charger see that? NO
    After how many charging procedures would YOU see this?
    What will happen if you charge a lipo several times with a damaged balancer plug?

    Dont get me wrong I also parallel charge all the time but
    this is an importan safety point where unfortunately nobody mention anywhere.

    Peter

    Reply
    1. Frank

      i think it is not serious fault.
      assume you para charge 2 packs of 4s battery, and balanced plug is damage (cell 1 of pack 1).
      in this case, cell 1 of pack 1 does not receive current from charger of course, cell 1 of pack 2 will be pumped double current ( but it is small current, for balancing).
      the pack 1 will be ok, just the cell not be balanced.
      i have checked voltage every get down from in the air, under 3.7 or over 3.8V
      So, if balance wire of a cell be broken, i will know when i put it in checker.

      Reply
  4. Jörgen

    Have you seen this banggood.com/ISDT-PC-4860-1-8S-Safe-Parallel-Board-XT60-CNC-Parallel-Charging-Board-p-1087255.html

    Reply
    1. Oscar Post author

      Yes i mentioned it in the review :) it’s a perfect companion with this charger as it comes with XT60 connector :)

      Reply
  5. Rox Wolf

    Also there are more advanced parallel boards with fuses for each plug, so if you miss to check the voltage, they will cut off the power and possibly save your battery with the board.

    Reply
  6. Anonymouse

    I think it is worthwhile mentioning that the batteries themselves might burn/blow up (all it needs is a small mechanical damage to create an internal short). The instructions usually have a big red warning not to leave the batteries unattended. So how do keep them?

    There are LiPo safety/guard bags on the market for charging and carrying batteries.
    Are they any good?

    Reply
  7. Blaise

    One thing I’m not entirely clear on: You Say ” Remember to always connect the main leads first, and then the balance lead. Because when you first connect the batteries together, the difference in voltage will cause a large current flow before they are equalized. ”

    Does the act of plugging them all in to the balance board do the equalisation or is there more to it?

    Also does the charger have to be plugged in for this to happen?

    Reply
  8. George

    I’ve seen too many people blow up their chargers because they don’t understand the power limits and I think it would be good to include something like this example;

    Assume that I am using the Turnigy Accucel-6 charger (rated at 50 W) and I have three 1300 mAh 3S LiPo batteries.

    I wish to charge each battery at a maximum rate of 1C or less, which is 1.3 A. 1.3 A * 3 batteries = 3.9 A total charge rate.

    Each cell will have a final voltage of 4.2 V so for a 3S battery, the final voltage is 12.6 V. Let us check to make sure that the power consumption will not exceed 50 W. 12.6 V * 3.9 A = 49.14 W, which is cutting it quite close to the limit. At least we can charge all 3 batteries at 1C.

    What would happen if I had four 1300 mAh 3S batteries?

    1.3 A * 4 = 5.2 A
    5.2 A * 12.6 V = 65.52 W.

    Odds are, the charger would blow up if I set it to charge at 5.2 A. This means that I have to select a lower charging rate; 50 W / 12.6 V = 3.968 A. The batteries will charge at a slower rate, but the charger will not be at risk.

    Reply
    1. Oscar Post author

      Thanks for the note, I will add some extra lines to point out the safety about charger power rating.
      I am using a computerized charger and it automatically sets upper bound limit on charger current. I might be getting too comfortable with this and forgot to mention the importance of correct charge current.
      I would also recommend everyone to get a charger that comes with this feature, it’s just so much safer and easier !

      Reply
    2. Miguel Santos

      I’m a novice, but….

      I have a Turnigy Accucel-6 50W 6A Balancer/Charger.
      I charge my 5000mAh 3S at 1C. rom your math above, i get 12.6V x 5A = 63 W (however, my Charger is rated at 50W).
      So…… how come it doesn’t blow up?!?!?

      Could it be because the amperage (A) the charger pumps in gets lower as the batteries build up voltage?

      Reply
      1. Oscar Post author

        The max current your charger can provide when charging 3S lipo is (50W/12.4V = 4A)
        Even if you want to charge the 5000mah at 1C (which is 5A), you wouldn’t be able to, your charger will automatically limit the charger current at 4A max, because it’s a computerized charger.

  9. Nano

    First check the voltage of each pack and equalize to about 0.2 difference. It’s on top of your post but this is good practice. More important use only similar packs to parallel charge!

    Reply

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