Review: Auline 6S 4000mAh 45A 21700 Li-ion Battery - For Extended Flight Times

Lithium-Ion (Li-ion) batteries are gaining popularity in the FPV drone community, prized for their higher capacity for the same weights compared to LiPo batteries. In this review, I’ll put the Auline 45A 6S 4000mAh Li-Ion packs to the test. We’ll delve into whether these packs live up to their capacity claims and assess their overall performance.

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Table of Contents

Where to Buy?

You can get the Auline 6S 4000mAh Li-ion battery from:

GetFPV: https://oscarliang.com/product-48sn
RDQ: https://oscarliang.com/product-2xmi
AliExpress: https://s.click.aliexpress.com/e/_DC36AFp
Auline: https://bit.ly/3Mmf895

Why Using Li-ion over LiPo?

In my Li-ion battery buyer’s guide, I’ve detailed the pros and cons of Li-ion batteries compared to LiPo: https://oscarliang.com/li-ion-battery-long-range/

To summarize, Li-Ion packs boast a higher energy-to-weight ratio than LiPo, but they come with a lower C-Rating. This means they offer more capacity than LiPo but has a limited top output current. Consequently, you’ll rarely see Li-ion batteries in racing drones. However, for extended flight times, they are an excellent choice. Long range FPV drones and fixed-wing aircraft are typically designed for efficiency, which translates to lower current draw, making Li-Ion batteries an ideal fit.

Auline, with its established reputation in the hobby community, stands out as a reputable supplier of quality FPV accessories, such as FPV backpack and batteries. It’s essential to choose a trustworthy battery brand as Li-Ion cells exhibit a wide range of quality, and with Auline, you are ensured quality and reliability in the product you are receiving.

Specifications

Cell Type: 21700 Li-ion (INR21700-45A)
Cell Configuration: 6S1P
Nominal Voltage: 21.6V (3.6V per cell)
Max Voltage (Fully Charged): 25.2V (4.2V per cell)
Rated Capacity: 4000mAh
Discharge Current (MAX): 45A
Maximum Charging Current: 4A (1C)
Battery Plug: XT60
Internal Resistance: 3.98mΩ (per cell)
Dimensions: 80x65x45mm
Weight: 398g per 6S Pack, 63.5g per cell

Quality and Construction

Upon arrival, the battery was securely packaged in bubble wrap within sturdy cardboard boxes, ensuring their safe transit.

These batteries are well constructed. They are wrapped in black PVC shrink wrap. Each pack is labeled with a detailed sticker that outlines its specifications, including cell configuration, rated capacity, maximum discharge current, nominal voltage, and watt-hour.

The battery comes with a standard 6S balance connector and an XT60 connector.

Most of Auline’s Li-ion batteries for long-range flying do not have BMS (battery management system), with the exception of their 4S 2600mAh battery pack designed for powering FPV Goggles. BMS is not desirable for powering aircraft because it shuts down the battery completely when voltage drops below certain level to prevent damage to the cells, something you want to avoid mid flight.

Bench Testing

Capacity

To assess the true capacity of the Auline 45A 6S 4000mAh pack, I discharged it until the voltage drops to 2.7V per cell. I used a discharge current of 2A (0.5C), which is low enough to minimize warming the battery and wasting energy.

The capacity measured approximately 3650mAh, not quite reaching the advertised 4000mAh, but still pretty good considering its high discharge rating.

Voltage Sag

To evaluate performance under load, I discharged the Auline battery at a 3C rate and compared it to the Lumenier 6S 3000mAh battery, also discharged at 3C. While this isn’t the most scientific comparison due to the Lumenier using 18650 cells, it’s the best available comparison I had at hand. Regardless I think it’s still an interesting test, the goal is to observe any differences in performance under the same C rating. Also I chose 3C discharge rate due to the limitation of my discharger, otherwise I would have chosen an even higher number.

As you can see the Auline shows up to 0.5V less voltage sag compared to the Lumenier, but the gap narrowed towards the end.

Internal Resistance

Another crucial aspect I measured was the internal resistance (IR) of the cells. Using my battery charger, which reports IR for each cell at the end of the charging cycle, I found the IR values to be slightly higher than the claimed 4mΩ, averaging around 7 to 8mΩ. While LiPo chargers might not offer the utmost accuracy in measuring IR, they provide a useful benchmark for comparison between batteries one owns. Based on these findings, the Auline battery’s IR is on par with that of Molicel P48B 21700, a leading option in long-range Li-ion cells.

Expanding Capacity with Parallel Connection

Auline provides a practical solution for those seeking extended flight times: an XT60 adapter that allows for the parallel connection of two batteries. By linking two Auline 45A 6S 4000mAh packs, you can effectively change the cell configuration from 6S1P to 6S2P. This clever setup doubles the capacity, increasing it from 6S 4000mAh to a substantial 6S 8000mAh.

Building Your Own Li-ion Packs

Building your own Li-Ion battery is also an option, I have a post dedicated to showing you how to do it using my own method: https://oscarliang.com/li-ion-battery-long-range/

My go-to cells are the Molicel P45B, popular for long-range quads due to their robust performance, offering 45A constant or 90A peak.

While building your own can be rewarding, it’s worth noting that it often costs as much as purchasing a pre-made battery. More importantly, building a battery pack can be hazardous and time-consuming if not executed correctly. If there’s any doubt or concern, I recommend opting for an off-the-shelf product for safety and peace of mind.

Conclusion

My original plan was to put this battery to the test on my 7″ FPV drone and fixed wings. Unfortunately, the weather hasn’t been cooperative, and each of these long-range flights usually take about an hour or longer. Since I’ll be away for a while, I’ll have to postpone further testing until my return. For now, I’m sharing the data I’ve gathered so far.

Based on my tests, the Auline’s Li-Ion packs seem to be an excellent choice for long-range applications. While they might come with a price tag of $69 each, and the idea of building your own packs might be tempting, the convenience, reliability, and quality assurance provided by AuLine’s offerings make them a strong contender.