Using Li-Ion Battery Pack for Long Range Flying

Li-Ion cells such as 18650 or 21700 have higher energy density than LiPo (more capacity mAh for the same weight), they make great battery for long range flying. I will recommend what to buy, and also show you how I built a 4S 18650 Li-Ion battery from scratch.

Here are my tips on long range FPV flying.

Buying Pre-made Li-ion Battery Packs

If you don’t want to make your own battery packs, you can just buy them off the shelf.

3S

4S

6S

The Pros and Cons of Flying Li-Ion Battery

Li-Ion battery has higher capacity than LiPo for the same weight. The 4S 18650 3400mAh I built, only weighs 203g, while a 4S 1600mAh LiPo has nearly the same weight. 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 however, it’s a great option because they don’t require a lot of current. If you use an efficient power system, Li-Ion cells are totally fine.

In fact, Li-Ion battery is popular in RC fixed wings / planes as they normally only use one motor. It’s also possible to use on highly efficient quadcopters. I am currently testing a long range quad that 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 pretty incredible!

Parts List To Build Your Own Battery

Here is the wiring diagram of a 4S Li-Ion battery pack with XT60 and balance connectors.

Note that there are two main types of Li-Ion cells we use, 18650 and 21700. The numbers are basically the dimension of the cell, 21700 is heavier and physically larger, so is its capacity.

I am using 18650 here because it’s more common and widely available online for purchase.

Sony VTC5A (US18650VTC5A) and VTC6 (US18650VTC6) are the popular choice and rated for 2600mAh and 3000mAh respectively. VTC5A has higher discharge rate (35A) than VTC6 (30A), but also slightly less flight time. I am using Panasonic NCR18650B in this build log just because I have some spare, and they do work fine for my setup. But try to get the VTC cells if you can, they do have better discharge rates.

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

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

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/

Edit History

  • Aug 2020 – article created
  • Mar 2021 – added product links to where you can buy Li-Ion packs directly

35 thoughts on “Using Li-Ion Battery Pack for Long Range Flying

  1. Tooraj

    hello and thanks Oscar,

    I bought a flywoo explorer and for it made my pack of Li ions. 4s 2200 mAh was the best I could get. Is that enough?

    and more importantly until what voltage do you continue to fly?
    for me the quad was alarming under 14v and I got nervous and landed.

    Reply
    1. Oscar Post author

      That’s a bit low for 18650 cells. You will probably only get 15 mins or so with that.
      I normally land when it gets to 2.8V per cell, some even wait until 2.5V which I think is a bit risky.
      You can set minimum voltage and warning voltage in Betaflight lower so it doesn’t alarm too early.

      Reply
  2. david thurman

    I have yet to find anything on the discharge rating calculation for lion batteries. Do i take the discharge amp rating per battery and multiply that against the Mah of the battery like we do with c ratings on lipos? So I am looking at 45amp 4200 molicel 21700 battery and as far as I can calculate a 6s can handle 189 amp max discharge. or slightly under 48 amps per motor if i am not mistaken. Is this correct?

    Reply
    1. Oscar Post author

      No, for Li-ion battery they should state the max discharge current in the data sheet?
      Lets say if it was 30A, if you connect 6 of them in series to make a 6S pack, the max discharge current is still 30A.

      Reply
  3. Raptor

    I want ask u… I have quad wizard x220.. not flywoo.. i have tried make 3s lithium ion battery..but my quad cannot fly for long time.. it less than lipo battery.. why my 3s battery lithium ion not effective to me?? I want to use lithium battery because i want more fly time.. 3s lipo only 5minit.. can u tell me why the reason…. Tq

    Reply
    1. Oscar Post author

      Old battery? fake capacity? You can test capacity, drain them down to 3V/cell, then charge them back to 4.2 and see how much mAh is put back.
      If capacity is too low, maybe get some new ones, I posted a link to them in the article.

      Reply
  4. Jonathan

    It would be awesome to get more photos or a better diagram of how you have the balance leads wired up. Other than that this is a fantastic, easy to digest, guide.

    Reply
    1. Oscar Post author

      I just charge them like lipo but with a low current (e.g. 1C), but this is just my way, not saying this is the right/safe way.

      Reply
  5. Jake

    Do the same rules for charing lipos apply to liion?

    Like what rate should I charge at? 3,000 mah 4d liion okay to charge at 3amps?

    What’s the best storage voltage?

    What’s the land voltage?

    What’s the max voltage?

    Reply
  6. Roy

    How long does yours take to charge?

    I built this and all the connections are good, with each cell showing as it should on the charger.

    I set my charger for Lithium Ion balance change, maximum 2 Amps. However it seems to be taking a very long time. Is this normal, or did I somehow overcook the cells?

    Reply
  7. Georgi Tushev

    The problem with using other cells is that is very difficult to find such with high “c” rating, let say 35-40Amps for Ok performance. I mostly use 21700 , they are as popular as 18650.

    Reply
  8. 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. 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
  15. 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
  16. 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
  17. 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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