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.
Further Reading: Here are my tips on long range FPV flying.
Differences Between Lipo and Li-ion
There are 3 main differences:
- Energy density
- Discharge rate
- lowest safe voltage
Li-ion battery packs are alternative to the most common Lipo batteries. Comparing similar size packs, Li-ion has about double the capacity.
LiPo batteries have much higher discharge rate than Li-ion, meaning you can get much higher current out of them. To give you an idea, typically a high quality LiPo have around 30C to 40C of continuous discharge rate, while Li-ion only has 5C (What’s C rating?)
Lastly, you can usually discharge a LiPo down to 3.5V per cell safely, however Li-ion can go much lower, e.g. 3.0V per cell. Both battery types can be fully charged to 4.2V per cell.
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. If you power an FPV freestyle drone with Li-ion, it will feel very weak and slow.
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 can totally handle it.
In fact, Li-Ion battery has been popular in RC fixed wings / planes as they normally only use one motor. It’s also possible to use on highly efficient quadcopters. I tested a long range quad that weighs under 250g. With a 4S 18650 Li-Ion battery I custom built, i was able to get nearly half an hour of flight time :) It’s pretty incredible! But it doesn’t have the power to perform crazy acro moves, I was only able to cruise around most of the times and do a few flips and rolls here and there.
What’s 4S1P and 4S2P?
4S is the nominal voltage of the pack, i.e. how many cells are connected in series. 2P is how many cells are connected in parallel. 4S1P has 4 cells while 4S2P has 8 cells in total. They both have the same nominal voltage, but 4S2P will be able to provide double the current, capacity and weight.
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.
- ZOHD 3S 3500mAh (Max 10A ): https://oscarliang.com/product-95k5
- Auline 3S 3000mAh (Max 30A): https://oscarliang.com/product-goi0
- Auline 4S 2600mAh (Max 35A): https://oscarliang.com/product-3lok
- GEPRC 4S 3000mAh (Max 30A): https://oscarliang.com/product-c4vy
- ZOHD 4S 5000mAh (Max 10A): https://oscarliang.com/product-idr5
- Auline 4S 6000mAh (Max 60A): https://oscarliang.com/product-lp7e
- Auline 6S 2600mAh (Max 35A): https://oscarliang.com/product-gtu2
- Auline 6S 3000mAh (Max 30A): https://oscarliang.com/product-zguf
- GEPRC 6S 6000mAh (Max 30A): https://oscarliang.com/product-ws6b
Things You Need To Build Your Own Li-ion 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 generally more common and widely available online.
Sony VTC5A (US18650VTC5A) and VTC6 (US18650VTC6) are the popular choices, with capacity of 2600mAh and 3000mAh respectively. VTC5A has higher discharge rate (25A) than VTC6 (20A), but slightly less flight time. I am using Panasonic NCR18650B in this build log only because I have some spare. They are okay for powering FPV goggles, maybe some low power builds too, but try to get the VTC cells if you can, they have much better performance.
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:
Buy 16 AWG Wires Here:
Buy Balance Connector Here
Buy Heatshrink Here
- Transparent Heatshrink (get the 86mm)
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.
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/
- Aug 2020 – article created
- Mar 2021 – added product links to where you can buy Li-Ion packs directly