LiPo Battery Parallel Charging Tutorial

Parallel charging is an efficient way to charge multiple LiPo batteries simultaneously. When it’s done safely, you can quickly charge many LiPo’s at the same time to minimize waiting given the short flight time FPV drones have.

If you are new to LiPo batteries, make sure to check out this guide: FPV Drone LiPo Battery Explained.

What is “LiPo Parallel Charging”?

Parallel charging is a fast and easy method to charge multiple LiPo batteries at once with just one single charger. The batteries are connected in parallel, hence the name “parallel charging”.

When charging batteries one by one, you have to repeatedly unplug a battery and plug another one in between charge. Parallel charging is way more convenient, as you only have to do this once.

Is Parallel Charging Dangerous?

When you connect two batteries in parallel, their voltage will attempt to equalize.

It’s like connecting two barrels at the bottom with a pipe, water from the fuller one will rush into the emptier one until the two barrels have the same amount of water. The same happens with batteries when you connect them in parallel, but when the voltage difference is too much, you can risk burning out the wires and overheating the batteries, even catching fire.

To safely charge batteries in parallel, you should only connect batteries of similar voltage level. The general consensus is, a difference within 0.1V per cell should be fine, that’s 0.4V for a 4S battery or 0.6V for a 6S. Note that the smaller the voltage difference, the safer it is.

A technique of mine before parallel charging is to sort them based on voltage. I have voltage labels on my charging bench and I put batteries of the same voltage in a pile, so I won’t forget.

When multiple batteries are connected in parallel, they effectively combine and become one big battery. The individual cells in each battery are also connected in parallel, so all the cell voltages will be balanced nicely too. To the charger, this is no different than charging one single battery.

parallel-charging-connection-diagram-battery-charger

Getting a Parallel Charging Board

A must have tool when it comes to parallel charging is a “parallel charging board”. These boards are designed to connect multiple LiPo batteries in parallel, and often has built-in protection such as fuses to prevent damage to the charger and the batteries due to current surge.

You have to plug both the main lead (XT30/XT60) and the balance lead from the Lipo battery in the parallel charging board.

A typical parallel charging board has enough slots to connect 4 to 6 batteries. More isn’t necessarily better, as it’s riskier, and it takes a more powerful charger to get the most out of it. In my opinion, 6 is more than enough for most pilots.

You will find many cheap and basic options like this, which I don’t recommend due to the lack of safety features. Yes they are cheap, but a simple user mistake such as plugging the balance lead in backward will burn out the traces on the board, and you’d have to buy another one. (I learned my lesson the hard way when I was a beginner)

parallel-charging-board-adapter-lipo-battery

Get a parallel board with fuses, like the ones below. This is what I used in the past and worked great.

Purchase:

If you want a higher quality parallel board, this is what I use right now – the ParaGuard by Lumenier. See my review for more detail.

Also available on Amazon (US): https://amzn.to/3hZRP45

And this is a cheap and small parallel board (on the left in the below picture). It has fuses for the XT30 connectors, but no fuse for the balance ports. However it has a voltage display as well as JST-PH connectors for your tiny whoop’s 1S LiPo’s which are very handy features.

product page: https://bit.ly/2ksvAux

What Charger For Parallel Charging?

You can use any LiPo charger that supports balance charging.

I am currently using the iSDT Q6 Pro and absolutely love it! Here is a list of chargers that I recommend and they are all great smart chargers fit for parallel charging.

How to Parallel Charging?

Parallel charging is a convenient way to charge your LiPo, but it’s also more prone to user-error than charging battery individually. Please do your research and ensure charging batteries safely. Here are some of the important tips you should bear in mind.

1. Precautions

It doesn’t matter how you are charging your LiPo, always keep a fire extinguisher near your charging station. I personally charge my batteries in an Ammo box (product page: https://amzn.to/3i4LkNo), it will help prevent a fire from spreading. Some recommend “LiPo bags” (product page: https://amzn.to/2YyS7Hp), but use these cautiously, many tests have proven them to be ineffective from preventing a fire.

2. Same Cell Count

Make sure all your batteries have the same cell count. E.g. you should only charge 4S batteries with 4S. If you accidentally connect a 4S with a 6S, you will get current surge and it’s not going to be pretty.

3. Brand, Capacity and C-Rating

It should be fine parallel-charging batteries of different brands and capacity together. However to ensure maximum safety, I only recommend charging batteries of similar spec, and capacity should be within a reasonable range. Anyway, use your common sense!

4. Check Voltage First!

Before plugging the batteries in the charging board, make sure you check the voltage of each battery first.

Make sure cell voltage difference is within 0.1V, that’s 0.4V for a 4S battery. If you want to play safe, you might want even smaller voltage difference. If a battery has vastly different voltage than the rest, you should just charge that one alone.

An easy way to do this is to use a LiPo voltage checker. They immediately display the voltage of each cell when you plug the balance lead in.

Or a fancy one like the iSDT BG 8S.

5. Connecting Balance Leads

Always connect the balance leads when parallel charging. This is no different than charging batteries individually. It prevents the charger from overcharging a particular cell.

6. Setting Charge Current Correctly

When charging a single LiPo pack, most people would charge at 1C to be safe. The charge current can be calculated as

Current = 1C x Capacity.

For example, to charge a 1500mAh pack at 1C, the charge current would be 1500mA, or 1.5A.

The same principle applies when charging multiple LiPo batteries, the only difference is that the capacity is now the sum of all batteries connected in parallel. For example if I have three 1500mah batteries, the total capacity is 4500mAh, and therefore the charge current would be 4.5A when charging at 1C.

7. Don’t Charge Damaged Batteries

We crash a lot with our FPV drones, and inevitably our batteries get battered and bruised.

You should never charge damaged and unhealthy batteries, not to mention parallel-charging them. Retire damaged LiPo as soon as you can, any time you charge them, there is a risk of fire.

Further Reading: When should I throw out LiPo?

Deformed LiPo batteries could be a sign of defected cells that results in higher internal resistance and significant increase in temperature during charging and discharging. And heat is the main cause of LiPo fires.

Further Reading: How to Protect LiPo from Physical Damage?

8. Don’t Go Away While Charging

Never leave LiPos charging unattended. You might be able to catch some signs of fire before it happens. For example, overheating, swelling and crackling.

Most LiPo fires could have been avoided if the person was there to stop the charging immediately and get the bad battery to a safe location.

9. Plugging  XT60 In First

Always connect the XT60 first, then the balance leads.

When you first connect the batteries together, voltage difference will cause current surge as they try to equalize. The balance leads are not rated for high current applications and could overheat and get damaged if current is too high.

And make sure you don’t plug the balance connector in backward, or you could melt the traces on a parallel charging board like the picture below.

para-board-trace-melt

Alternative to Parallel Charging

Multiple-channel chargers are thought to be an alternative to parallel charging.

There are chargers with multiple output channels. These are designed to charge multiple batteries at the same time.

Some people prefer multi-channel charger over parallel charging because they believe it’s safer as the batteries are not connected at all. Also they allow you to charge batteries of completely different specs, including type, cell count and voltages, so arguably it’s way more convenient.

But the number of batteries you can charge simultaneously is limited by the number of channels, which is usually two. There are four-channel chargers, but they are very expensive.

Check out this basic and affordable 4-channel charger we reviewed before –  SkyRC E4Q.

Edit History

  • Dec 2014 – Article created
  • Oct 2016 – Updated equipment options
  • Nov 2017 – Article revised
  • Jan 2019 – Article updated
  • Mar 2019 – Added image how I group batteries based on voltage
  • Jun 2020 – Re-wrote guide, added ParaGuard

36 thoughts on “LiPo Battery Parallel Charging Tutorial

  1. richard welch

    if i have 3 lipo batteries in parallel each cell is 2000ma, and voltage is down to 3.2v per cell.
    how much charge would go into the batteries to fully charge them. ? 2amp or 6amp

    Reply
  2. Dick MOger

    What is the problem with, say, treating two 2s LIPOs wired in series as a single 4s LIPO? Sure the cells have to balance, but using two identical Lipos should do it… The Neg lead on the second LIPO balance lead will be redundant as the neg is connected to the plus of the first battery. Surely all the charger will see is a single 4s 14.8v lipo with a balance lead connected for each individual cell….

    What is the issue here as surely this is simpler and safer this way round than charging them in parallel?

    (I have two rx type 2s 1800mah lipos in series to power a small electric motored locomotive that consumes less than 1 amp)

    Reply
  3. Charel

    Hi Oscar,

    i have a specific question to the calc you do in the following paragraphe:

    “———————————————-
    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.
    “———————————————–

    When you assume instead of charging 3x3S -> 4x3S, how is your voltage going to change, isn´t in paralell the voltage staying the same for lets say 3x3S Lipo and 4x3S, it stays at 12,6V, or am i missing sth, i cannot understand this 5.2A for 4x3S Lipos instead of 3,97A when cell voltage should stay the same?

    Thank you in advance.

    Reply
    1. Oscar Post author

      When adding an extra battery in parallel charging, voltage doesn’t change, but the total current if you still want to charge them at 1C.
      The total capacity has increased from 3 batteries to 4. To charge this at 1C, the required current has also gone up (as well as power).
      If the charger can’t support the higher power, you will have to lower the charge current, therefore you can no longer charge at 1C.

      Reply
  4. 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. Eric Roberts

      No, charger stays on 3s! When batteries are connected in parallel (like we charge) the amperage is combined. When batteries are connected in series the voltage doubles. Exp: a 3s battery is 3 batteries in series and the voltage is 3x a 1s.

      Reply
  5. 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
  6. 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

  7. 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
  8. 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. 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.

  15. 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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