Parallel charging is a time-saving method for charging multiple LiPo batteries simultaneously, perfect for FPV pilots dealing with short flight times and lengthy charging process. This tutorial will cover the essentials of parallel charging, including safety precautions and recommended parallel charging boards, to help you optimize your charging experience.
For those new to handling LiPo, explore our comprehensive battery guide: https://oscarliang.com/lipo-battery-guide/
Table of Contents
What is LiPo Parallel Charging?
LiPo parallel charging is an efficient method for charging multiple LiPo batteries simultaneously using a single charger. By connecting the batteries in parallel (hence the name parallel charging), you can eliminate the need to repeatedly unplug and plug batteries during the charging process.
In a parallel charging setup, LiPo batteries are connected through a parallel charging board, effectively forming a larger battery with a combined capacity while maintaining the original voltage. For example, if you are charging six 6S 1500mAh LiPos on a parallel charging board, it’s the same as charging a single 6S 9000mAh battery.
The individual cells in each battery are also connected in parallel, allowing for balanced cell voltages across all batteries. From the charger’s perspective, this setup is no different than charging a single battery.
Choosing the Right Parallel Charging Board
When parallel charging, a parallel charging board is a must-have tool for safely connecting multiple LiPo batteries in parallel. These boards typically include built-in protection features, such as fuses, to prevent damage to both the charger and batteries due to current surges.
To parallel charge, simply plug both the XT30/XT60 connector and the balance connector from the LiPo battery into the parallel charging board. Most boards accommodate 4 to 6 batteries, which is sufficient for the majority of pilots.
Although there are many cheap and basic options available, we recommend selecting a board with safety features to minimize the risk of user errors. A basic, budget-friendly board with fuses, like this one, is a good starting point.
Get it from these vendors:
- RDQ: https://oscarliang.com/product-ru2m
- BuddyRC: https://oscarliang.com/product-fmoc
- Amazon: https://amzn.to/3wa5mfa
- Banggood: https://oscarliang.com/product-n4ac
For a more advanced option, consider the HGLRC Thor 6 Pro, which supports 2S to 6S LiPo, has both XT30 and XT60 connectors, and includes fuses. It can charge up to 6 LiPo batteries at once. This is what I personally use currently, read the full review here: https://oscarliang.com/hglrc-thor-pro-6-parallel-charging-board/.
You can get it from:
- AliExpress: https://s.click.aliexpress.com/e/_DBIr25r
- GetFPV: https://oscarliang.com/product-sln3
- RDQ: https://oscarliang.com/product-k0l6
- Amazon: https://amzn.to/3zXIUu4
- Banggood: https://oscarliang.com/product-7qe7
Choosing the Right Charger for Parallel Charging
Any LiPo charger that supports balance charging can be used for parallel charging. However, a powerful charger helps you fully capitalize on parallel charging and significantly speeds up the process. Don’t forget to check out my recommended chargers: https://oscarliang.com/choose-lipo-battery-charger-power-supply/#Top-LiPo-Charger-Recommendations
During parallel charging, the output current from the charger is distributed among all connected batteries. A charger with a higher output current can greatly accelerate the charging process. For example, to charge six 6S 1500mAh LiPos at 1C, your charger should be capable of providing 9A of charge current (6 x 1.5A). You can charge at a rate lower than 1C, but it will take longer to fully charge the LiPo.
In the same scenario, you need a charger rated with at least 226.8W output (25.2V x 9A) to supply the necessary 9A current. If your charger is rated at 200W, you can only charge at 7.9A (200W / 25.2V), which is effectively 0.88C.
Important Rules to Follow when Parallel Charging
Charge in a Fireproof Place
Always keep a fire extinguisher nearby when charging. Personally, I charge my batteries in an ammo box (a metal box): https://oscarliang.com/lipo-battery-guide/#Ammo-Box. While some recommend using “LiPo bags” (https://oscarliang.com/lipo-battery-guide/#LiPo-Safe-Bags), many tests have proven them to be ineffective in preventing fires.
Only Connect LiPos of the Same Cell Count
When you connect a 4S and a 6S LiPo in parallel, the current from the 6S LiPo will flow to the 4S until their voltages equalize. However, this will overcharge the 4S battery, potentially causing it to explode. The current surge can also overheat the battery, electrical wires and may cause the solder joints to melt.
Only Connect LiPos with Similar Voltage
When two LiPo batteries with significant voltage differences are connected in parallel, the higher voltage LiPo will charge the lower voltage LiPo until their voltages equalize. This will cause a current surge which is bad for the batteries and your charging board.
Before plugging the batteries into the charging board, check each battery’s voltage. Personally, I always ensure the cell voltage differences is within 0.1V per cell (e.g., 0.4V for a 4S battery, 0.6V for a 6S battery). If a battery has a significantly different voltage than the rest, charge it separately. Connecting batteries with similar voltage levels ensures a safe parallel charging process.
I use a LiPo voltage checker for quickly checking battery voltage by plugging in the balance lead. Here are some options: https://oscarliang.com/fpv-tools/#LiPo-Voltage-Checker
Purchase a basic voltage checker:
- AliExpress: https://s.click.aliexpress.com/e/_DFDd8MZ
- GetFPV: https://oscarliang.com/product-kejx
- RDQ: https://oscarliang.com/product-ky5p
- Amazon: https://amzn.to/3aC3Avn
For a more advanced option: https://oscarliang.com/toolkitrc-mc8/
A technique I use before parallel charging is to sort the batteries based on voltage. I have voltage labels on my charging bench, and I place batteries with the same voltage in a pile, ensuring I don’t forget their respective voltage levels.
Connect the Main Plug First
Always connect the XT60 plug first, followed by the balance leads. When initially connecting the batteries, voltage differences can cause a current surge as they attempt to equalize. Balance leads aren’t rated for high current applications and may overheat or get damaged if the current is too high.
Connect the Balance Plug Correctly
Always connect the balance leads during parallel charging, as this is essential to prevent overcharging individual cells. Be cautious about polarity, as connecting batteries with the wrong polarity can cause shorts and fires.
I recall using a charging board without fuses many years ago and accidentally plugged in the balance connector the wrong way round. The copper traces melted instantly due to the mistake, emphasizing the importance of fuses in preventing such accidents.
Only Charge LiPos with Similar Capacity
You should only parallel-charge LiPo batteries of similar capacity. You might get away with charging LiPo batteries with slightly different capacities, but it’s a good practice to charge those with similar specifications for safety. Use your common sense!
Setting Charge Current Correctly
When charging a single LiPo pack, most people would charge at 1C for safety. 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 connected batteries in parallel. For example, if you have three 1500mAh batteries, the total capacity would be 4500mAh, and the charge current would be 4.5A when charging at 1C.
Don’t Charge Damaged Batteries
Crashes are inevitable with FPV drones, and our batteries can become battered and bruised. You should never charge damaged or unhealthy batteries, especially not in parallel. Retire damaged LiPo batteries as soon as possible, as there is a risk of fire each time you charge them.
Further Reading: When should I throw out a LiPo: https://oscarliang.com/when-retire-lipo-battery/
Deformed or puffy LiPo batteries could be a sign of defective cells, resulting in higher internal resistance and a significant temperature increase during charging and discharging. Heat is the primary cause of LiPo fires.
Further Reading: Ways to Protect LiPo from Physical Damage: https://oscarliang.com/protect-lipo-battery/
Don’t Leave Charging Unattended
NEVER leave LiPo batteries charging unattended. You might be able to detect early signs of potential fire, such as overheating, swelling, or crackling. Most LiPo fires could have been avoided if someone was present to stop the charging immediately and move the problematic battery to a safe location.
Alternatives to Parallel Charging
Multi-channel chargers are considered a safer alternative to parallel charging. These chargers allow you to charge multiple LiPo packs simultaneously without connecting them through a parallel charging board. Since the LiPo packs are not connected, many believe this method to be safer.
Chargers with multiple output channels are designed to charge several batteries at the same time. Furthermore, multi-channel chargers enable you to charge batteries with different types and specifications, unlike parallel charging, which requires similar voltage levels and the same cell count for each LiPo pack. However, multi-channel chargers can be expensive, and the options are quite limited.
The ToolkitRC M4Q is a good 4-channel charger (review): https://oscarliang.com/toolkitrc-m4q-charger/
Check out my LiPo Charger recommendations: https://oscarliang.com/choose-lipo-battery-charger-power-supply/#Top-LiPo-Charger-Recommendations
Conclusion
In conclusion, parallel charging is a valuable technique for FPV drone pilots to charge multiple LiPo batteries efficiently. By following essential safety guidelines and understanding the principles of parallel charging, you can maximize its benefits. Alternatives like multi-channel chargers offer added convenience and safety. Choose the right method based on your specific needs and budget.
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
- Apr 2023 – Updated guide and product links
51 comments
We need to charge 8 batteries that are 12s. I can’t find anything premade. Have you ever heard of something like this?
Cheers
I have a similar charger to the one you have… If I use the dji 3 battery board, will it still only charge one at a time?
Is the negative side of a balance wire coming from a lipo always on the same end every time on all lipos 3 to 6s and is it on the same spot on all chargers that has the balance charger port
Yes, always on the same end.
Super helpful! Thank you
Okay I parallel charge 6S lipos using my Icharger 4010 duo and the odd time I accidentally try to plug the balance lead in the wrong way round and it can burn the pins on the charging board….but on close inspection the pins don’t actually line up to touch!!! After looking at how it burned the pins out on the board I was surprised at what I found!!!
It’s actually the back of the balance lead where you can see each wire connector in the plug…..when the balance plug is inserted at an angle the contacts will actually touch the pins ?
I’m now going to cover each of these openings on each of my lipos balance leads…
If your wondering how the hell I managed to put the balance plug in the wrong way round and at an angle …I was wearing my Sunglasses and I’m long sighted ..
So glad I finally found how to stop this happening again.
Hope this helps others.
Is the charging board stil safe to use after melting one tiny trace on it?
Very good know how on Lipo charging in parallell!
You have on both sides the cell cable pluggs and the xt60 is in the middle. Do I have to plug in the cell cable pluggs on the right or left side?
Any recommended IR differences between packs? I want to make sure while parallel charging; that I do not damage a once healthy battery from a bad battery in the bunch.
When you plug a 2S balance lead into these 6 pin ports, which end do you line it up with?
you can only plug it in one way
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
6 Amp..
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)
Replying a comment that 1 year old but anyway,
I also considered series charging quite a lot,
And I think the downside of it is
limited maximum voltage.
Most chargers can charge only 6~8S,
So with 3S + batteries, only 2 of them can be charged. And 4S or 6S batteries cannot even charged with series.
I’m not sure if diffrent capacity batteries can be
charged series, but I think voltage diffrence,
and even diffrent cell count won’t be a problem.
Btw for 1~2S whoop or toothpick batteries,
I think series charing harness(or board) is worth to make one DIY.
So if i have one 4S with 3.90V and one 4S with 3.75V i am all good?
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.
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.
Oh, so the 0.2 voltage margin should be for the whole pack, not per cell? Is that correct?
0.2V difference for the whole pack :)
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 !!!????
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.
Thanks for the response i am glad i waited to find out , and not find out the hard way !!!
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.
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.
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.
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?
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
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
yes they will try to even out the difference in voltage
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.
Yea :) charge current can be as low as you want, only going too high can cause problems.
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..
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.
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
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.
Have you seen this banggood.com/ISDT-PC-4860-1-8S-Safe-Parallel-Board-XT60-CNC-Parallel-Charging-Board-p-1087255.html
Yes i mentioned it in the review :) it’s a perfect companion with this charger as it comes with XT60 connector :)
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.
Very good point there Rox!
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?
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?
it does. The board will connect the battery as one single battery without the charger turning on.
When you say “connect the main leads before the balance leads”, is that per battery? Ex. I plug in main lead, then the balance lead. then move on to next battery? or do i plug in all the main leads of all the batteries first, then all the balance leads of all the batteries?
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.
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 !
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?
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.
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!
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.