If you are just starting out with 5-inch FPV drones, you might find it challenging to decide whether to use a 4S or 6S LiPo battery. In this post, I will explain the differences and help you make an informed decision.
Further Reading: New to FPV drones? Take a look at our beginner’s guide.
Pro Tip: Betaflight has introduced a new feature that allows powering a 4S quad with a 6S LiPo battery by reducing motor output.
Here’s a list of my favourite 6S and 4S LiPo batteries.
Table of Contents
Benefits of 6S Over 4S
A 6S LiPo battery has a 50% higher nominal voltage than a 4S due to two extra cells. The maximum voltage of a 6S is up to 25.2V, compared to 16.8V for a 4S.
The potential improvements from using a 6S over a 4S include (some of these points might be up for debate):
- LOWER amp draw
- LESS voltage sag
- LONGER flight time
- MORE responsive and agile performance
Lower Amp Draw?
One of the most significant advantages of 6S over 4S is the lower current required to produce the same power.
Power is voltage multiplied by current: P = V x I
For example, to produce 1000W, it takes nearly 60A on 4S (at 16.8V) while it’s only under 40A on 6S (at 25.2V).
Lower amp draw results in:
- Less stress on the battery
- Reduced “voltage sag” throughout the flight
- Less energy loss in the wires due to resistance, though this is often negligible
Check out some DVR footage of a 6S quad:
Is 6S Better for Your Battery?
The lower amp draw means your batteries run cooler during flight, which is beneficial for battery longevity. This also allows the use of lower C rating packs for the same power, potentially saving costs by selecting less expensive cells.
However, to match the weight of a 4S battery, we often choose lower capacity batteries, which can limit the maximum discharge current, since battery capacity is a factor in maximum discharge current. So, higher C rating packs might still be necessary.
Max Discharge Current = C Rating x Battery Capacity
Responsiveness
Due to less voltage sag under load, the motors maintain consistent acceleration, enabling them to change RPM more rapidly and consistently. This results in an overall more responsive and agile aircraft. The faster RPM change rate significantly affects the handling of your quad.
Higher Efficiency?
There’s a controversial theory that a 6S FPV drone offers longer flight times than a 4S.
This isn’t necessarily true, as we often select 6S batteries of similar weight or watt-hours (Wh) as 4S batteries. To achieve similar speeds on a 6S, the motors need to spin at comparable RPMs, requiring a similar amount of power. Therefore, theoretically, flight times should be comparable to those of a 4S when flying at the same speed.
Longer flight times with a 6S are possible by reducing motor power (e.g., using lighter props or adapt a less aggressive flying style) or using larger battery packs with higher energy capacity. However, either approach will inevitably impact aircraft performance.
The benefit in flight time is more likely to be seen in AP (aerial photography) platforms, where motor speed is more consistent, and rapid RPM changes like those in racing drones are less frequent.
But why are there people claiming they are getting longer flight time on 6S than 4S? Maybe it’s due to the lower current in the system, which leads to less overheat and overall higher efficiency. However this benefit might not be noticeable in most cases.
Is 6S Faster?
A 6S quadcopter, with specially selected components, certainly have some advantage over a 4S (as demonstrated by most professional racers have now switched from 4S over to 6S batteries). However, in drone racing, race tracks often feature numerous turns and gates, requiring as much pilot skill as raw speed, if not more.
The lower current draw and lower voltage drop of 6S give racers more room to experiment with motor and prop combinations. This flexibility allows for more strategic choices in finding the best balance between efficiency and performance based on the specific race track.
Choosing Motors for 6S
There are two sides to the argument when selecting motors for a 6S FPV drone. Some recommend lower KV motors to match the theoretical max RPM of 4S-equivalent motors, while others suggest using similar KV motors as on 4S to fully utilize the extra power from 6S batteries.
I will experiment with both ideas in my testing.
Lower KV Motors
For a safer and more efficient setup, choose a low KV motor that provides a theoretical max RPM in the same range as an equivalent 4S setup using a common KV rated motor.
| 4S – KV | 5S – KV | 6S – KV | RPM (VxKV) |
| 2300 | 1840 | 1533 | 38640 |
| 2400 | 1920 | 1600 | 40320 |
| 2500 | 2000 | 1667 | 42000 |
| 2600 | 2080 | 1733 | 43680 |
| 2700 | 2160 | 1800 | 45360 |
| 2800 | 2240 | 1867 | 47040 |
| 2900 | 2320 | 1933 | 48720 |
| 3000 | 2400 | 2000 | 50400 |
| 3525 | 2382 | 2350 | 59220 |
With more volts in the system, you can execute the KV more effectively. In fact, you might need even slightly lower KV than calculated to achieve the same RPM in flight. For example, 1600KV on 6S might equate to not 2400KV on 4S, but actually slightly higher such as 2500KV.
As KV increases, the torque rating is said to decrease. However, from my observations, voltage sag is a more influential factor, preventing you from reaching the theoretical max RPM on 4S. That might be why some people claim 6S feel “more punchy”.
With a 6S setup, I also noticed the ability to swing a heavier prop more effectively (e.g., higher pitch props). If I were using a 4S LiPo, most high KV motors wouldn’t have the power to swing a heavy prop at high RPMs like on the 6S setup.
Here are my motor recommendations.
Running 6S LiPo on 4S Motors
I tested 4S motors (2350KV) on 6S batteries.
These motors are considered ultra high KV for 6S, and they did provide brutal straight-line speed and impressive cornering. However, the downsides were significant: severe voltage sag and terrible inefficiency. The motors also became extremely hot after a short flight. Personally I would avoid using 4S motors on 6S batteries, motors could easily get damaged.
However, Betaflight offers a solution to reduce motor output, which allows you to power 4S quad with 6S LiPo by setting motor output to 66%.
How About 5S?
Well, the cell count and voltage of 5S are in between those of 4S and 6S, so you can expect its performance to also be intermediate. However, 4S and 6S batteries are more widely available, making 5S batteries relatively rare.
Conclusion
Personally, I prefer 6S mostly for the reduced voltage sag. Apart from that, I don’t feel it’s significantly different from 4S in other aspect. Oh, how many people still remember the discussion back in 2014/2015 when we were deciding between 3S and 4S? It seems we are still moving up in voltage. Maybe in the future, 8S or even 12S will become common – who knows? :) Update – Here’s a new article discussing the possibility of using 8S Lipo in FPV drones in 2023: https://oscarliang.com/8s-fpv-drone-2023/
Edit History
- Feb 2018 – article created
- Jan 2020 – added info about running 6S on 4S motors
- Dec 2023 – updated article
24 comments
and the only sane reason i stay in 4s is the price and weight. im broke. lol. but i did love the punch outs and viceral feel of 6s quad.
think your theory only applies if the 6s vs 4s both have the same drone weight, the same motor, the same mah, the same prop.
Especially the theory that says the use of low amperage for 6s, you don’t calculate the large momentum due to the weight of the heavier drone, maybe you try to just fly around, not in race mode … I think in 6s race mode it will drain tons more ampere than 4s (same drone, difference in lipo weight)
second, why do the 6s beginner pilot racer always use an esc of at least 40a? because the heavy load on the esc for 6s …. unless you are a pro, because pro pilots are able to compensate for the momentum of the weight quad
Btw, in sorry if i wrong, and Iscar liang alwats ny favorite…
Exactly, the voltage drop is given by the current density on the battery electrodes (approx. current / cell capacity) as the chemical reactions are not fast enough to keep the potential. Since the cell weight is proportional to its capacity, a 6s battery has 4/6 cell capacity as well as 4/6 current draw of the same weight and the same C rate 4s battery generating the same power, of course. This results in a similar current density and voltage drop. The only difference I can see from the physics point of view is slightly more efficient wiring of lower KV motors causing less heating, and more importantly, the heat loss in the cables and electronics that is quadratically proportional to the current.
As usual, you make some great points. But there is one thing that really confuses me about motor selection. FYI, I am in the process of building a S500 size camera drone. I really want to use 6s. But it’s tough to find low enough Kv motors that can handle 6s. But my question is. Why do the motor test data sheets always seem to point to 4s being more efficient than 6s? Even though we know that 6s should be more efficient, theoretically.
Great work!
The 6S versus 4S debate is correct in thought but uses the wrong words. Specifically:
– 6S is less efficient than 5S, which is less efficient than 4S
… proven in all tests using 4″ props to 48″ props
… proven in all tests using 10A to 80A ESCs
… proven in all tests using motors from 20 grams to 600 grams
– 5S and potentially 6S might, however, give longer flight times. What? Why?
… we just set the world record for electric powered multicopter at 4 1/4 hrs
o beating the old record by more than two hour
o more than doubling the old record
… using a 6S which was less efficient than 5S which was less efficient than 4S
… but the ship drops out of the sky when below 15 volts
o so a 4S would only use a small portion of its 16 to 10 volt range
o and a 5S would use a portion of its 21 to 12.5 volt range
o but uses all of the 6S range
o so in some cases, a 5S or 6S battery ends up with more usable watt capacity than a 4S
o despite being less efficient
Tests show that efficiency drops about 1.5% for every 1 increase in S.
Actually I am not convinced that 6S is more efficient than 4S. As you said, for the same amount of Energy to be translated into Speed you’d have less amp draw. Though there are additional factors to take into account here:
First: to have the same power to weight ratio as the 4S setup (and we’d have to assume exactly the same components to have the same test conditions. Same Frame, etc.) we need to have smaller capacity cells. While I think the added Material such as more balancer cables, separating material and so on are negligible there is another effect. You’d need a very high C-Rating on the smaller cells for them to be able to sustain the Amps needed. While you don’t need as much current, it would still heavily tax the batteries. The best currently available Cells are in the 1300~1800mAh range. Everything below 800mAh starts to greatly decrease in performance/real C-Rating.
Second: For a lower kv Motors you need more windings. More windings result in thinner copper wires and thus in an increased internal resistance. A higher internal resistance then again results in more losses to heat.
I have made the reverse test. I built a 3S quad with handwound 4100kv Motors and while Amp draw really skyrockets, the results in flight performance are almost equal to the 2600kv 4S variant I built before that. In the end it’s more an issue of optimization of the several parts rather than the numbers of cells. That’s my observation at least.
As current draw is lower when running at higher voltage, less heat should be produced due to resistance in the battery? I’m not sure that this is true it’s more of a questions…
I suspect there are so many variables at play it’ll be hard to answer efficiency of a real quad in flight.
FWIW – I’m interested in 6S to be able to punch harder without battery alarms – hence why I’m looking into this and found this page. That should be easier to verify (I hope)
@Oscar – great article as always! Thanks for your contributions to the hobby!
A lot of pilot’s running 6s are running 1300mah packs. That would be running close to a 1900mah+ pack on 4s. The quality of the cells are a lot lower on 6s and when voltage drops to low, puff (damage) happens.
I believe the only difference in efficiency would be less heat generated in the wires and ESC (both depend on current only), but motors and battery efficient would be the same. overall, the difference would be very small in my opinion.
Hi Oscar,
I disagree with following statements:
less stress placed on your battery
less “voltage sag” for the duration of the flight
They would be true only if the both batteries would have same capacity, that is the 6S would be much heavier than 4S. In real world, you should compare batteries with the same weight, lets say 1000mAh 6S vs. 1500mAh 4S , where above statements would not be true. Both have cca 25kJ of stored energy and for 65C cells, produce about 1600W. In fact, its almost irrelevant for the battery if you have 1S 6000mAh or 6S 1000mAh, they will have the same output power at the same load (C-rating). In fact, the more S you use, the more wires/welds/separators must be used, so purely from the battery perspective, 6S would be slightly more heavy than less 4S battery with the same output power.
Check my spreadsheet to check output power for 3S and 4S: docs.google.com/spreadsheets/d/10v60jHFL6-ocdkE_nku2GTTjnM14L6x5lH2uh5teTAI/edit?usp=sharing
What I wanted to say is that power density [W/kg] is not depended on number of cells, but only on C-rating and cell weight.
Wow your spreadsheet is sick dude! Nice work there!
Hey Oscar, nice blog.
Do you know of anyone who has used a high kv motor on 6s?
6S is more efficient than 4S because as you need less Amps for the same power, you loose less energy in heat in the whole system. The system run cooler at the same amount of power. For the increase responsinevess it is due to the fact that you reduce your Kv, so you moteur have more torq.
Pth= Ri²
Hi Oscar, thanks for this very interesting article. I just noticed on my latest built that all my electronics can handle 6s. So it is tiggling me a bit to try it. I have T-motors 2204 2300kv there. So I was wandering if they would handle the load. The setup is a 4inch speed addict 180, Kiss Esc 24A RE, Kiss FC v1. 0, Matek PDB, Tramp Hv VTX, FOXEER Arrow V3 cam, XSR… What do you think?
What happened to 5S? We just stepped over 5S’s cold lifeless corpse to 6S?
5S has the same properties as 6S, but just not as extreme :) I only wanted to try 6S because I want to see the extreme :)
Oscar, great article. If you do keep the weight the same, and go from 4s to 6s pack, and you draw the same power out of the battery, you are using the same percentage of the C rating of the battery. I’ll put the math in a link here:
docs.google.com/spreadsheets/d/1kQpCmVJGBKKjdaE0T78ketV4vH1u47xri0Im9LDtmzE/edit?usp=sharing
This is exactly what I was thinking. You are effectively plugging different values into an equation to reach the same figure. There has to be a reason why it is more efficient… if it actually is. I’m wondering if gains are found by there being less heat loss (heat loss = wasted energy) due to lower amperage?
I believe the only difference in efficiency would be less heat generated in the wires and ESC, but motors and battery efficient would be the same. overall, the difference would be very small in my opinion.
Yes I agree, I did mention that in the article as well :)
Great entry! Thank you for the valuable insight and collecting the knowledge in one place again!
What was the cost of that build?