Parallel charging allows you to charge multiple LiPo batteries at once using a single charger. Parallel charging is an effective way to quickly charge the amount of LiPo’s that mini quad pilots use. When you do it properly, it’s not particularly dangerous and actually brings benefits too.
If you are new to LiPo batteries used on quadcopters, make sure to check out our guide first: Quadcopter LiPo Battery Explained.
Why Parallel Charge LiPo Batteries?
You can charge your batteries in parallel with a powerful charger, which is way faster than charging them individually. Of course you can buy multiple less powerful chargers and charge them individually too, but it’s not as cost effective as parallel charging.
Parallel charging is very convenient as it saves you from having to unplug one battery to connect another to the charger.
Is Parallel Charging Risky?
When you plug 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 until the two barrels have the same amount of water.
The same happens with batteries when you connect them in parallel if the voltage levels aren’t the same. If the voltage difference is too great, the equalization current can be high enough to burn out wires, overheat the batteries, or even make batteries explode.
To safely charge batteries in parallel, you should only connect batteries of similar voltage level. As a guideline, a difference within 0.1V per cell should be fine. The smaller the voltage difference, the smaller neutralization current and it will be safer.
Getting a Parallel Charging Board
The safest way to parallel charge is to use a dedicated “parallel charging board”. These boards allow you to connect and charge multiple LiPo batteries simultaneously.
Ideally you should get one with built-in protection – inline automotive fuses or poly fuses that protect against excess current flow.
Normally parallel charging boards have enough slots to connect at least 4 to 6 batteries. A LiPo battery should have a discharge lead (the main plug), and a balance plug. You have to insert both connectors into the parallel charging board.
You will see this type of cheap and basic options a lot, but they don’t have any safety features built-in.
I personally recommend using a parallel board with fuses, like the one below. This is what I personally use for years and it’s been working great.
What Charger Do I use?
The Basics Rules/Tips of Parallel Charge
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
You might be able to get away parallel charging batteries from different manufacturers and of different capacity. However we do recommend only charging batteries of similar spec to ensure maximum safety (preferably even the same brand, model and batch).
However different capacities within a reasonable range should be okay. Slight differences in C-Rating should also be okay.
4. Check Voltage!
As mentioned earlier, you should check the voltage of each battery you are about to parallel-charge.
Make sure the 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 you have a battery with vastly different voltage than the rest, you should put that aside and charge it alone.
Get a voltage checker, so you can check the voltage of each cell in a lipo battery simultaneously by plugging in the balance lead. I personally use these and really like them:
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. Don’t Charge Unhealthy Batteries
We crash a lot with our mini quads, and inevitably we batter and bruise our batteries.
You should never charge unhealthy batteries – not to mention parallel-charge it. Any time you charge an unhealthy LiPo, there is a risk of fire. 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.
8. Watch Your Batteries
Never leave LiPos charging unattended. You might be able to catch some signs of fire before they happen – overheating, swelling and crackling. A lot of LiPo fires could have been avoided if the person was there to stop the charger immediately and get the battery to a safe location.
Tips on Plugging in Batteries to Parallel Board
Always connect the discharge leads first, and then the balance leads.
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).
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.
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.
There are chargers with multiple channels (separate outputs) that allow you to charge multiple batteries at the same time without connecting them together. Many people prefer this over parallel charging because they believe it’s safer, and just as fast. Also they allow you to charge batteries of different cell count and voltages so arguably it’s more convenient.
Check out this basic and affordable 4-channel charger we recently reviewed – SkyRC E4Q.
- Dec 2014 – Article created
- Oct 2016 – Updated equipment options
- Nov 2017 – Article revised
- Jan 2019 – Article updated