Building 4S 18650 Li-Ion Battery Pack for Long Range Flying

As Li-Ion cells have higher energy density than LiPo (more capacity mAh at the same weight), they make great battery for long range flying, in this post I will show you how I built a 4S 18650 Li-Ion battery.

Here are my tips on long range FPV flying.

Disclaimer: Soldering on battery is dangerous, if you decide to follow instructions in this post, do so at your own risk.

You can also buy this pre-made I believe, I will try to test some and see if they are worth recommending. For now I am making one with the cells that I trust :)

The Pros and Cons of Li-Ion Battery for Flying

Li-Ion battery has a higher capacity than LiPo for a given weight. The 4S 18650 3400mAh I built, only weighs 203g, while a 4S 1600mAh LiPo weighs nearly the same. On paper you should get double the flight time!

However, the maximum discharge rate of Li-Ion battery is not great compared to LiPo, that’s why it’s not a popular battery choice for FPV drones.

For long range aircraft which don’t require a lot of current, with an efficient power system, Li-Ion cells are totally fine.

In fact, Li-Ion battery is popular in wings as they only has one motor. It’s also possible to use on highly efficient quadcopters. I am currently testing a long range quad which weighs under 250g. With the 4S 18650 Li-Ion battery I built, i am able to get nearly half an hour of flight time :) It’s incredible!

Parts List

The following photo is the wiring diagram of the Li-Ion cells, XT60 and balance connector. If you can understand this diagram, you should have an IQ in the top 2 percent :)

You can use other Li-Ion cells, but 18650 is the most common size and widely available online.

Sony VTC5A (US18650VTC5A) and VTC6 (US18650VTC6) are the popular choice and rated for 2600mAh and 3000mAh respectively. I think VTC5A has higher discharge rate but slightly less flight time. I am using Panasonic NCR18650B in this build log as I have some spare, and they do work like a charm for my setup.

Buy 18650 Batteries Here:

You will also need some wires (I am using 16AWG for the discharge lead and 20AWG for balance lead), as well as 5-pin balance connector and a XT30 or XT60 connector. XT30 should be fine, but XT60 might be more convenient if that’s what you use on the drone.

Buy XT30 Connectors Here:

XT60 Connectors

Buy 16 AWG Wires Here:

Buy Balance Connector Here

Buy Heatshrink Here

How I Built 4S 18650 Battery

Solder wires to the connectors, I use longer wires than I need, and I can just trim them to the length I want later.

Soldering wires to the 18650 cells according to my wiring diagram. You should definitely check out my tutorial on how to solder 18650 batteries safely.

Here’s the top side.

Here’s the bottom side.

Cover all solder joints with electrical tape then finally wrap it in heatshrink. And yes, you can probably use a shorter discharge lead to save a couple of grams, I made it longer on purpose.

Even smaller than my 4S 1500mAh LiPo pack.

The 4S 18650 battery weights 203g, and I get about 30 mins of flight time from it on the Flywoo Explorer LR 4″: https://oscarliang.com/flywoo-explorer-lr/

21 thoughts on “Building 4S 18650 Li-Ion Battery Pack for Long Range Flying

  1. Jose Cuevas

    Hey if I were to wire the balance lead reversed would it make my isdt charger give an error code? It’s giving balance lead voltage too high.

    Reply
  2. ORastah

    Hello I’m starting too, I don’t know much about it, but I would like to know if using the 3400 mha 3.7 battery, I can use 9900 mha 3.7 to further increase the autonomy of flight

    Reply
  3. Dustin T

    Hey Oscar, thank you for the write up! I am impatiently waiting for my explorer LR HD to be delivered. Plan on assembling a few of these packs and had a few questions:

    1) Should I be looking at protected or unprotected 18650s? I plan on assembling just as you did in this tutorial.

    2) what is the lowest amp rating for a 4s 18650 pack you would run on the explorer? As I understand, there is a trade-off between a higher mAh vs discharge amperage. I am willing to sacrifice a little flight time if it means that performance will be unaffected vs running a lipo. I’m totally new to FPV so pardon my ignorance.

    Thanks!!

    Reply
  4. Fabian

    Things I thought about, maybe someone can help:
    1. How much is the current-draw difference between 3s and a 4s battery for 3″ quads. Lower voltage->more current (p=u*i). But also lighter. Any experiences?
    2. Do you think that 0.1*7mm nickel-strips and the spot-welded “spots” will sustain the ~10A current. Not sure if i should spotweld or solder the batteries…

    Happy flying together

    Reply
  5. Bruce Robinson

    What is your best guess at the “C” rating of this pack and is the balance lead used when you charge on your ISDT in Li-Ion mode? I have a Hitec X2 that has a Li-Ion mode. Do you know if it will work the same way as your ISDT?

    Reply
  6. Christian Markussen

    If you do not want to solder the cells then you can buy assembled packs and attach you own lead and balancing connector. Here is a link to AliExpress using the 18650 VTC6 cells rated for 30A. I have ordered two packs and will try them out on the Explorer that I just ordered.

    aliexpress.com/item/4001140540403.html

    Reply
  7. Jesper

    Thank you so much for your content, Oscar.

    This was just what I needed in preparation of my Explorer, while it makes it’s way through corona-slowed international post. I have started backing you on Patreon, because your content is truly remarkable. Also enjoy it’s written.

    TO ALL WHO USES OSCARS CONTENT: Back him on Patreon. It must require tons of work, which saves us tons of time and mistakes. Goto: https://www.patreon.com/oscarliang

    Reply
  8. MJW

    Hey Oscar, thanks for this article! Very interesting.

    Question, being that this li-ion 4s battery build has an XT-60 connector, can you charge this on the typical chargers we normally use for Lipo (assuming the charger has a li-ion setting) or do you need to use a different type of charger?

    Thank you

    Reply
    1. Oscar Post author

      I personally use iSDT chargers, and they have Li-Ion mode.
      I see people charging them in LiPo mode, but do this at your own risk :)

      Reply
  9. Azurflying

    only for 1806 motors or below for 5 or 4 inch, and very light weight quad. More than 20 mn flight time, with all my own packs since 2 years. 2.9v max low limit. Works fine, but very gentle on the throttle.

    Reply
  10. CESAR FIERRO MONTALBA

    hi Oscar.

    I have a doubt about the discharge current, I bought the following batteries from TBS to make a 4S2P 18650 battery. But it only has 10A drain current. is it enough or should I consider a more current one.

    team-blacksheep.com/products/prod:lg18650

    Reply
    1. Oscar Post author

      Depends on how much current your model draws when cruising.
      For example my quad draws 6A and 10A con. discharge should be fine.

      Reply

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