Long-range FPV drone flying requires batteries with high energy density for extended flight time, Li-ion batteries are an excellent choice for this purpose. In this tutorial, we will discuss the pros and cons of using Li-ion battery packs compared to LiPo batteries, focusing on flight performance, weight, flight time, and cost. Additionally, we will explore the options of purchasing a ready-made Li-ion battery or constructing one yourself using high-discharge 18650 or 21700 Li-ion cells.
Further Reading: Here are my tips on long range FPV flying.
Differences Between LiPo and Li-ion Batteries
Lithium-ion (or Li-ion) battery packs serve as an alternative to the more common LiPo batteries.
Three main differences distinguish these battery types:
- Energy density
- Discharge rate
- Lowest safe voltage
LiPo batteries have a much higher discharge rate than Li-ion, meaning they can provide a significantly higher current output. For example, a LiPo battery typically has around a 50C continuous discharge rate, while Li-ion batteries only have around 5C (Learn more about C rating here: https://oscarliang.com/lipo-battery-guide/#C-Rating).
Here’s a demo of my 4″ Flywoo Explorer achieving 30 minutes of flight time using a 4S 18650 Li-ion pack:
Another distinction is the safe discharge voltage. You can generally discharge a LiPo battery down to 3.5V per cell safely, whereas Lithium-ion batteries can go much lower, e.g., 3.0V per cell. Both battery types can be fully charged to 4.2V per cell.
Pros and Cons of Using Li-ion Battery Packs
Increased energy density and flight time
Li-ion battery packs offer higher energy density than LiPo batteries, meaning they store more energy per unit of weight. This results in longer flight times for long-range FPV drone flying. Comparing similar size packs, Li-ion has about double the capacity than LiPo.
For example, a 4S 18650 3400mAh Li-ion battery weighs around 200g, while a 4S 1600mAh LiPo has nearly the same weight. On paper, you should get double the flight time!
Lower discharge rate
Li-ion batteries typically have a lower discharge rate (C-rating) than LiPo batteries. This means they may not be able to provide the high current demands required for aggressive, high-performance flying and punches. While Li-ion batteries are not a popular choice for freestyle and racing, they are an excellent option for long-range that don’t require a lot of amp draw, such as cruising and relaxing flight. If you use an efficient power system, Li-ion cells can sufficiently handle the demands.
Higher initial cost
Li-ion batteries are more expensive to purchase. However I personally found them to last much longer than LiPo. Firstly, you crash less with Li-ion because the flight you do with them tend to be slow and steady. Secondly, they have metal housing which make them a lot more robust against physical impact. So in the long run they are actually more econmical.
Understanding 4S1P and 4S2P
If you’re not familiar with LiPo battery terminology from our beginner’s tutorial, let’s revisit the meanings of S and P in battery specifications.
The S in 4S represents the number of cells connected in series. Conversely, the P in 2P signifies how many cells are connected in parallel. A 4S1P configuration consists of 4 cells connected in series, while a 4S2P configuration contains 8 cells in total. Although both configurations have the same nominal voltage, a 4S2P battery can deliver double the current, capacity, and weight compared to a 4S1P battery assuming they are using the same cells.
Buying Ready-Made Li-ion Battery Packs
Ready-made Li-ion battery packs are available for purchase, providing a convenient option for those looking to quickly incorporate Li-ion batteries into their long-range FPV drone setup.
2S 2500mAh 18650 (25-30A):
2S 3000-3500mAh 18650 (10-30A):
- BuddyRC: https://oscarliang.com/product-m2c8
- GetFPV: https://oscarliang.com/product-pnk
- NBD: https://oscarliang.com/product-92oh
2S2P 5000mAh 18650 (50A):
- BuddyRC: https://oscarliang.com/product-qffk
3S 2500-2600mAh 18650 (25-35A):
3S 3000mAh 18650 (30A):
- NBD: https://oscarliang.com/product-syqo
- RDQ: https://oscarliang.com/product-8po5
- GetFPV: https://oscarliang.com/product-goi0
3S 3500mAh 18650 (10A – for fixed wings):
3S 4200mAh 21700 (45A):
4S 2500-2600mAh 18650 (25-35A):
- GetFPV (Auline): https://oscarliang.com/product-3lok
- GetFPV (Dark): https://oscarliang.com/product-vrl0
- RDQ: https://oscarliang.com/product-o0ug
- BuddyRC: https://oscarliang.com/product-gxdy
4S 3000mAh 18650 (30A):
- NBD: https://oscarliang.com/product-7dno
- GetFPV: https://oscarliang.com/product-c0ng
- RDQ: https://oscarliang.com/product-a5x6
4S 3500mAh 18650 (10A – for fixed wings): https://oscarliang.com/product-l8h0
4S 4200mAh 21700 (45A): https://oscarliang.com/product-j0br
4S 5000mAh 21700 (10A – for fixed wings): https://oscarliang.com/product-idr5
4S2P 8400mAh 21700 (45A): https://oscarliang.com/product-ir4q
6S 2600mAh 18650 (35A):
- NBD: https://oscarliang.com/product-81wt
- GetFPV (Auline): https://oscarliang.com/product-gtu2
- GetFPV (Dark): https://oscarliang.com/product-ehyj
6S 3000mAh 18650 (Max 30A):
6S 4200mAh 21700 (45A): https://oscarliang.com/product-3fvc
6S2P 5200mAh 18650 (70A): https://oscarliang.com/product-i6gr
6S2P 6000mAh 18650 (30A): https://oscarliang.com/product-ws6b
6S2P 8400mAh 21700 (45A): https://oscarliang.com/product-qu7g
Building Your Own Li-ion Battery Pack
DIY Lithium-ion battery packs with individual 18650 or 21700 cells can be a cost-effective and customizable solution. By choosing specific cells and assembling the battery pack yourself, you have full control over the battery’s quality, capacity, discharge rate, and overall performance. However it requires decent soldering skills.
Below is a wiring diagram for a 4S Li-ion battery pack with XT60 and balance connectors.
Pay close attention to the wire order on the balance connector.
FPV pilots commonly use two types of Li-ion cells: 18650 and 21700. They are the same type of battery, just different in size. These numbers represent the dimensions of the cell, with 21700 cells being heavier and larger but offering greater capacity and discharge rate.
To ensure optimal performance and safety, select high-discharge 18650 or 21700 Li-ion cells from reputable manufacturers.
Popular 18650 cell choices include Molicel P28A, Sony VTC5A (US18650VTC5A), and VTC6 (US18650VTC6), with capacities of 2800mAh, 2600mAh, and 3000mAh, respectively. The VTC5A has a higher discharge rate (25A) than the VTC6 (20A), but slightly shorter flight time. Molicel P26A and P28A are the newer options that offer similar performance to the VTC5A, typically at a lower price.
Molicel P26A/P28A 18650:
- RDQ: https://oscarliang.com/product-1np7
- GetFPV: https://oscarliang.com/product-ghz0
- Amazon: https://amzn.to/3A99ocl
Sony VTC5A 18650:
Sony VTC6 18650:
Molicel P42A 21700:
- RDQ: https://oscarliang.com/product-pgng
- Amazon: https://amzn.to/3MDKDw7
- GetFPV: https://oscarliang.com/product-7xgt
Molicel P45B 21700: Link to be added later.
You’ll also need wires (I recommend using 16AWG for the discharge lead and 20AWG or 22AWG for the balance lead), a 5-pin balance connector, and either an XT30 or XT60 connector. The XT30 is an excellent choice due to its lighter weight and capability to handle the low amp draw. Choose an XT60 if that’s the connector type used on your drone, or use an XT30 to XT60 adapter if needed.
- RDQ: https://oscarliang.com/product-6gvi
- GetFPV: https://oscarliang.com/product-0ipn
- Amazon: Amazonhttps://amzn.to/3l8PdY0
- Banggood: http://bit.ly/2zTIRD6
- AliExpress: https://s.click.aliexpress.com/e/_DkJfemp
- RDQ: https://oscarliang.com/product-xzn1
- GetFPV: https://oscarliang.com/product-hwx7
- Amazon: https://amzn.to/3l6oonc
- Banggood: http://bit.ly/2AuxHnC
- AliExpress: https://s.click.aliexpress.com/e/_Ddy57H7
16 AWG Wires
- AliExpress: https://s.click.aliexpress.com/e/_DFtzaZX
- Amazon: https://amzn.to/3Jfu0DE
- Banggood: http://bit.ly/2ALByxa
- GetFPV: https://oscarliang.com/product-z3it
- RDQ: https://oscarliang.com/product-wj65
Balance Connector Here
- Aliexpress: https://s.click.aliexpress.com/e/_DezrpZB
- Amazon: https://amzn.to/2AlClFK
- GetFPV (4S): http://bit.ly/2K01jtT
- GetFPV (6S): https://oscarliang.com/product-8nsa
Heatshrink Tube (86mm for 4S 18650)
XT30 to XT60 Adapters
How to Make a DIY Li-ion Battery
Disclaimer: Soldering on batteries can be dangerous. If you decide to follow the instructions in this post, do so at your own risk.
Start by soldering wires to the connectors, using longer wires than necessary so you can trim them to the desired length later.
Next, solder the wires to the 18650 cells according to the provided wiring diagram. Use good quality solder with flux core, avoid using additional acid based flux (solder paste) as it will corrode the connection/battery in the long run. See my solder recommendation here.
Before soldering, use sandpaper to scratch the top and bottom sides of the cell. This will help the solder adhere better.
“Tin” both sides of the batteries with a small amount of solder, allowing it to cool down before soldering the wires.
Keep the time your soldering iron touches the battery terminals to a minimum. The longer the iron is in contact with the battery, the more heat will build up. To accomplish this, use a powerful, temperature-controlled soldering iron. A less powerful iron won’t maintain its temperature as effectively since the heat will be absorbed while soldering large pieces of metal. I personally use the TS100 iron, which works exceptionally well.
Here’s the top side.
Here’s the bottom side.
Cover all solder joints with electrical tape, and then wrap the entire assembly in heat shrink. While you could use a shorter discharge lead to save a couple of grams, I made mine longer on purpose.
The finished 4S 18650 battery weighs around 200g and provides over 30 minutes of flight time on my Flywoo Explorer LR 4″: https://oscarliang.com/flywoo-explorer-lr/
Betaflight Misreading Cell Count on Li-ion Batteries
A common issue with Li-ion batteries is that their voltage can drop significantly lower than traditional LiPos, leading to Betaflight sometimes misreading the number of cells.
This becomes problematic if you’re monitoring voltage per cell on your OSD. Take a 6S Li-ion battery as an example: when its voltage falls below 18.0V (3V per cell), Betaflight may mistake it for a 5S battery, showing an incorrect per-cell voltage of 3.6V. This misleading readout could tempt you to fly longer than you should.
To prevent this, you can lock the cell count in Betaflight by using the CLI. Simply enter:
set force_battery_cell_count = 6
By doing this, you’ll ensure Betaflight keeps a consistent cell count during your flight.
Li-ion battery packs offer significant advantages for long-range FPV drone flying, such as increased energy density and extended flight times. Despite some trade-offs like lower discharge rates and a higher initial cost, the benefits often outweigh the drawbacks. Building your own Li-ion battery pack can be a cost-effective and customizable solution for those looking to optimize their drone’s performance. However, for those who lack soldering experience, purchasing ready-made battery packs off the shelf may be a safer and more convenient option.
- Aug 2020 – article created
- Mar 2021 – added product links to where you can buy Li-Ion packs directly
- Apr 2023 – updated tutorial and product links