LiPo Battery Parallel Charging Tutorial

Parallel charging allows you to charge multiple LiPo batteries at once using a single charger. Parallel charging is a more effective and faster way of charging your batteries, and it allows you to go out and fly more often, which is what this is all about.

If you are new to LiPo batteries used on quadcopters, make sure to check out our guide first: Quadcopter LiPo Battery Explained.

Getting a Parallel Charging Board

Normally parallel charging boards have enough slots to connect 4 to 6 batteries. Each battery has one discharge lead (main plug), and one balance plug, you need to insert both connectors into the para-board.

The following para-board is the most basic and cheapest option, but it doesn’t have any safety features built-in.

parallel-charging-board-adapter-lipo-battery

I personally recommend using para-boards with built-in fuses like the one below. They cost a bit more, but the extra safety is well worth it.

Here are some good ones:

Why Parallel Charge LiPo Batteries?

Charging your batteries in parallel is faster than charging them individually given your charger is powerful enough.

It allows you to maximize the output power of a single charger while we charge small batteries such as 1300mAh. They only take 1.3A to 2.6A each assuming you charge them between 1C to 2C.

Parallel charging is also convenient as it saves you from having to unplug one battery to connect another to the charger.

The best way to parallel charge your battery is by using dedicated “Parallel Charging Boards” (para boards). These boards allow you to connect and charge multiple LiPo batteries simultaneously.

Good quality para boards are equipped with fuses which mean they cut off the connection if there is a problem. This is an essential safety feature that minimizes the risk of damaging your battery and causing a fire.

Parallel Charging vs. Dual Channel Chargers

Multiple channel chargers allows you charge multiple batteries at the same time without connecting multiple batteries together. Many people prefer that over parallel charging because they think it’s safer, and just as fast.

It will be another article to discuss the safety claim, but is it really just as fast?

Serious FPV pilots can charge between 8 and 12 packs simultaneously. That means you can charge a whole session of batteries in the time it takes a dual charger to charge 2 packs.

parallel-charging-lipo-battery-power-quadcopter

Before You Parallel Charge, Read This

So parallel charging is a great way to charge your LiPo, but it’s also more prone to error than charging a single battery. Please do your research and ensure you charge your batteries safely.

Here are some important points you should understand and follow.

1. Safety and Precaution

It doesn’t matter how you are charging your LiPo, always keep a fire extinguisher near your charging station. More importantly, always use a metal box (or Ammo box) to store your batteries while charging which can minimize the chance of fire spreading.

2. Same Cell Count

Your batteries have to have the same cell count. For example, you should only charge 3S batteries with 3S, 4S with 4S and so on.

3. Capacity and C-Rating

We recommend only parallel charging batteries of the same capacity and C Rating to ensure maximum safety (preferably the same brand and model).

However slightly different capacities within a reasonable range should be okay. For example, you might be able to get away from parallel charging a 4S 1500mAh with a 4S 1600mAh.

Slight differences in C-Rating should also be okay, some LiPo batteries advertise that they can be charged at a higher rate than 1C, but we still only recommend parallel charge Lipo batteries at 1C or lower to minimize risk.

4. Voltage Level

Voltage in a battery is like water in a barrel, if you connect 2 barrels together, water from the fuller one will flow into the emptier until the 2 barrels have the same amount of water. If you have 1 full barrel and 1 empty, the water will flow with the weight of a full barrel behind it which could burst a pipe.

Likewise, before connecting the batteries together, you should always check if their voltages and ensure they are at a similar voltage level. They don’t have to be the exact same voltage, small differences are allowed. Generally a difference within 0.2V is acceptable.

When connecting multiple batteries together, the voltage difference between them will be neutralized. But if the voltage difference is too large, it will cause a high current to flow between battery packs as they try to equalize, like bursting a pipe, this could burn your parallel board, the battery wires, or even the batteries.

If you have a battery with vastly different voltage, you should isolate it and charge it alone.

5. Plug in all the Balance Leads

Always hook up the balance connector for every battery before charging. This is no different than charging you batteries individually.

This will allow the charger to monitor the individual cells to avoid overcharging, even though they’re connected in parallel and appear to the charger as one large cell.

6. Charge Current

When charging a single LiPo pack, I usually just charge at 1C, and the charge current can be calculated as

Current = 1C x Capacity.

For example, to charge a 1800mAh pack, I will use 1.8A; Or for an 800mAh pack, I use 0.8A. You can choose to charge at higher C rate if your batteries allow, but it increases the risk.

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 2000mah batteries, the total capacity is now 6000mAh, and I can charge them at 6A.

7. Battered Batteries? Don’t Risk It

We crash a lot with our mini quads, and inevitably we batter and bruise our batteries.

My advice is to bin those damaged batteries and don’t risk it.

Deformed LiPo batteries could have defected cells that have much higher internal resistance resulting in significant temperature increase during charging and discharging. And heat is the main cause of many LiPo fires.

How to Parallel Charge LiPo Safely

Now you understand the requirements for parallel charging, let’s talk about how to do it.

Firstly you will need get a decent parallel charging board (aka para-board), see our recommendation at the beginning of this article.

Using a parallel charging board

When charging, I always put the para-board and batteries in a fire-proof container, such as a metal ammo box, this helps reduce the risk of fire.

LiPo fire during charging is very rare, I personally have been using LiPo batteries since 2013 and not yet had a fire caused by charging. But still, it’s better safe than sorry.

You must make sure that the power connectors on your para-board match the ones on your batteries (the ones in the picture are XT60). If your batteries have a mix of different types of connectors (e.g. JST, T-connector), you can just get adapters for them instead of a whole new board.

Getting a voltage checker

Another must-have tool for parallel charging is a voltage checker, which allows you to check the voltage of each cell in a lipo battery simultaneously. I personally use these and really like them:

Understand the Max Charging Current

Modern LiPo chargers are smart enough not to go over the maximum current allowed depends on the rated power, even if the user sets a higher current. The maximum charge current of the charger can be calculated using this equation:

I = P/V

If your charger doesn’t have this feature you might want to manually calculate the safe charging current before connecting the batteries.

Calculate Max Charging Current

Assuming that I was using the 50W Turnigy Accucel-6 charger, and I want to parallel charge three 3S 1300 mAh LiPo batteries.

If I want to charge my batteries at 1C, the charging current would be 3.9A. But does my charger support this amount of amps? Let’s find out.

Beware that battery voltage increases during charging, while the power is a constant, the maximum current allowed decreases. Again, smart chargers can automatically adjust the current appropriately without any human intervention.

So for those dumber chargers, you might have to manually change the charge current constantly. But that’s not ideal, it’s probably easier to just set the lowest charge current, which is when voltage is at the highest, i.e. at 4.2V per cell. For a 3S battery, this is 12.6V.

The maximum charging current the charger can handle is:

50W / 12.6 = 3.97A

So we are all good! But what happens if we had 4 batteries instead of 3? Well we simply can’t charge at 1C as the charge current would be 5.2A, and it would exceed the power rating of the charger.

 

Most smart LiPo chargers these days can automatically calculate all this for you. It sets an upper limit to the charge current for safer charging, even if you set it to a higher value, it won’t go above that limit. Therefore I strongly recommend spending a little extra to get a decent charger, it’s just so much safer and easier!

I am currently using the iSDT SC620 charger, and absolutely love it! Here is a list of chargers that I recommend and they are all smart chargers.

Tips on Plugging in Batteries to Para-Board

Remember always connect the discharge leads first, and the balance leads after.

When you first connect the batteries together, a difference in voltage will cause a current flow before they are equalized, the larger the voltages, the higher the current that will flow.

The balance leads are not rated for high current and could easily overheat and get damaged. The current surge could even melt the traces on the parallel charging board (it happened to me a while ago as shown in the following photo).

para-board-trace-melt

Always balance charge when parallel charging, and remember to plug in the balance leads on every pack so that every cell in every pack is balanced before, during and after charging.

Make sure you are plugging in the balance lead in the correct orientation. Even though they are designed so that you can only plug it in one way, it’s possible to make enough contact with the wrong pins to cause sparks.

 

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 multiple LiPo batteries are connected to a parallel charging board, they will be charged and balanced nicely. You might wonder how it works.

parallel-charging-connection-diagram-battery-charger

When they are connected in parallel, separate batteries become one big battery. As we mentioned earlier, the moment you connect them, there is a surge of current flow to equalize the voltage differences, and their voltages will become the same across all the packs.

But how does cell balancing work during charging? Similar to the above, the individual 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 have their voltages “evened out”, and again it acts like a single LiPo battery.

That’s it!

It’s not unheard of for a LiPo to catch fire while charging, especially when you have multiple batteries sitting next to each other, this can be very dangerous!

It is good practice to remain in the room where your batteries are charging, and always make sure that they are all disconnected from the charger before going out.

If you decide to go ahead with parallel charging, 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.

Edit History

  • Dec 2014 – Article created
  • Oct 2016 – Updated equipment options
  • Nov 2017 – Article revised

30 thoughts on “LiPo Battery Parallel Charging Tutorial

  1. Michael Benjamin

    So if i charge two 3s 450 mah batteries would i set the charger to 0.9amp , 6s battery on the charger? been keeping it at 3s and just realized if it’s see’s it as one battery 3s+3s=6s… that i could be charging at that instead !!!????

    Reply
    1. Oscar Post author

      No, when two 3S batteries connected in parallel, it’s still a 3S battery, but the capacity is combined, so you have a 3S 900mah instead.
      So you can charge it with 0.9amp, and set the charger to 3S.

      Reply
      1. Michael Benjamin

        Thanks for the response i am glad i waited to find out , and not find out the hard way !!!

  2. David Burkhart

    Pavan Shetty: Yes, any number of batteries in parallel will attempt to equlize (or charge each other) until the voltage potentials between them is 0…even to the detriment of the batteries involved. This is precisely why Oscar Liang and anyone else who have experience with these suggest quite strongly that you carry a voltage checker and use it after each discharge. Personally, I don’t, I use an annually calibrated multimeter and check each cell after every flying session and keep logs of each flight including cell voltage, flight time and mAh’s discharged. This is also to monitor battery health.

    Reply
  3. Chris

    Why have we not made a device to balance cells in flight? I balance charge all the time but it seems a few transistors should be plugged into the balance lead to keep each cell within .05v and only move charge from one cell to another under flight conditions to extend flight time and pack life. We all have that one cell that could use the help of its neighbor I think.

    Reply
    1. Thomas H

      My thoughts ever since lipo’s hit the market:

      1. If theres such a fuss over the risks during charging (that ultimately all come from a cell being overcharged due to the other cells not being at the same voltage caused by resistance difference) then why isnt the battery fitted with the balance circuit?

      2. in what ungodly parallel dimension was it a good idea to stray away from the historical standard format where the battery simply has discharge poles and the appliance has the lead wire if not a standardized battery interface docking (like almost every frigging other type of battery ever conceived!)

      3. And who the hell came up with the stupidity to attach the charge wires (balance leads) to the battery and the fixed connector on the charger!? OMG someone tell these people they are doing it the wrong way around!! nobody needs charging cables in flight!? we need them only at the charger! for the love of god please tell me there is in fact some twisted reason for this nonsens!

      4. if the cells of a lipo become unstoppable firebombs when the pouch is pierced and oxygen can react with the chemicals inside, wouldnt it have been a jolly good idea to exclusively market these things in a decent dent-proof enclosure?? and while we’re at it, lets integrate a balance circuit and discharge socket in that casing too.. eh?

      Reply
      1. JayMax

        1. A balance circuit is built in to most chargers. Some Lipo batteries have balance circuits, but this adds cost and weight and is another component that can fail or become damaged Some people choose not to balance charge or buy chargers without a balance port. Both lipos with balance circuits and chargers with balance ports are very rare because there is very little demand for them. Straight lipos and balance chargers are safely used by the vast majority of people. In many (but not all) cases where lipos fail, proper safety measures haven’t been followed. In other cases defective equipment could be at fault – just look at exploding segway/hover/balance board batteries due to poorly designed charging circuits.

        In your example checking a Lipo before charging with a simple $2 cell checker or cheap multimeter would avoid potential issues. If you don’t know the charge state of a Lipo, don’t charge it.

        2. I’m not sure what you mean by standardized battery interface docking. 9v batteries are different to AA batteries. Most cameras or phones with removable batteries have different interfaces. Lipo batteries vary tremendously in cell count, capacity, size, shape, discharge rate and use. All lead to different solutions, but one constant is the balance connector which almost all Lipos use. When it comes to connectors the differences are easily and routinely overcome with adaptors or by soldering new connectors. In any event, it’s usually not difficult to find a Lipo for most applications with the correct connectors.

        3. Having balance wires on the battery keeps the size of the pack down. A fixed female balance connector would add at least 5mm to the size of a battery pack. This is quite a lot, particularly on smaller packs. The balance leads we have now are sometimes used as an alternative power feed are also quite easy to fix. Still, there are Lipos with female balance connectors, but they tend to be hard case packs for use in RC cars. There are weight, size and cost implications and soft case packs are still popular despite lots of hard case options being available. Lastly, it’s harder to tell if a cell is starting to swell if it’s enclosed in a hard case.

        4. As above, there are hard case packs available, predominantly for RC cars. For flight applications in particular, weight is a primary concern and hard case packs, where available and suitable, still aren’t very popular. Even in RC cars they aren’t all that popular – many are only bought to comply with competition regulations such as ROAR. Lipos are largely about getting as much energy and current from as small and light a package as possible.

        Much of what you ask for is already available. You made reference to flight so many of the drawbacks I’ve mentioned apply. Depending on the size and voltage you use, you may find some suitable hard case options. Just search in broad terms including the words hard case and you might find something to suit. Also think outside the box. If you have a requirement for 4S packs you could use 2 x 2S saddle packs in series.

        At the end of the day though, market forces shape the supply chain and you will find that the best options are the ones that are most widely available. Lipo safety is more about education than it is about the technology.

        JayMax

  4. 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
    1. Scott

      Curious…can I assume the C charge rate is a “not to exceed” value? In such case there is no issues with slow charging a lipo 11.1v 5200mAh 57.7wh 2C charge rate using the 1A setting as opposed to a 5A charge? I see none. But curious what your take is. I have found using lower charge rates extends battery life. Just beginning with the lipo.

      Reply
  5. 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
    1. will

      Hi Punkie,

      I’m trying to put a compact solar charging / battery // converter system together for my RV.. any ideas?

      I want to get away from the “big battery” scene.

      Reply
  6. 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
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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.

  12. 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
    1. David Buxton

      My parallel charging boards come with poly-silicon fuses which almost instantly go to high resistance when they get hot with too much current. Let them cool down and ready to go again. No need to replace burned out fuses.

      One reason why you want reasonably well matched batteries, in terms of charge voltage, is that batteries suffer when charged too fast. So the higher voltage battery might happily surge out 50 Amps but the receiving battery is briefly getting charged way too fast. So it would seem better to plug in the balance leads first, but only if the board has poly fuses which will slow down the current if the match is off a bit too much.

      Reply

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