Fxlion BM-HV300 293Wh B-Mount Lithium-Ion Battery for ARRI ALEXA 35 Review

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The Fxlion BM-HV300 293Wh B-Mount Lithium-Ion Battery was designed specifically for the ARRI ALEXA 35.

Key features

  • 28.8V for ALEXA 35
  • B-Mount Interface, SMBus Communication
  • 10A Maximum Load
  • 2 x D-Tap Ports: 16V, 60W Maximum
  • 2 x USB Ports: 1 x USB-A & 1 x USB-C
  • 5-LED Status Indicator
  • Contoured, Easy-to-Grip Form
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Now, there are a lot of dual voltage battery solutions on the market that will work with the Alexa 35, so you may be thinking why go with a native 28.8V battery? Well, while there is certainly nothing wrong with dual-voltage batteries, you may well prefer to just go with a native 28.8V B-mount battery if you are buying it specifically for the ALEXA 35. Sure, you could buy a dual-voltage B-mount battery, but then you would also need to buy an adapter plate to use it on select cameras and some lights. Currently, there are no products or cameras apart from the ALEXA 35 that natively use B-mount.

The voltage operating range for the ALEXA 35 is 20.5-33.6V. The Fxlion BM-HV300 has a voltage of between 24-33.6V. What this means is that it can keep powering the ALEXA 35 even when it drops to its lowest voltage and is almost fully discharged. This is not the case with a battery like the Anton/Bauer Dionic 26V Lithium-Ion Battery as its voltage range is 17.5-28.9V. Once it reaches a certain level of discharge it will actually cause the ALEXA 35 to shut off even though it may still be showing that it has 20% capacity left. With the ALEXA 35, you really need to use a battery that has a minimum operating voltage of above 20.5V.

If you want to buy batteries that you can use on multiple platforms, at least in my opinion, it probably makes more sense to go with a dual voltage V-mount or AB-gold mount and use an adapter plate. Although, in saying that, you can also purchase B-mount plates that allow you to run dual-voltage B-mount batteries on other cameras and equipment.

The downside to a 28.8V B-mount battery as I just mentioned, is that you can currently only use it natively on the ALEXA 35. That does somewhat limit its versatility.

Size & Weight

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The Fxlion 293Wh B-Mount battery tips the scales at 1.68 kg / 3.7 lb. This is slightly higher than some other competing batteries.

Fxlion BM-HV300 293Wh3.7 lb / 1.68 kg
SWIT HB-A290B 290Wh 28.8V3.35 lb / 1.52 kg
Core SWX Helix Max 275 Lithium-Ion
Dual-Voltage Battery
3.1 lb / 1.4 kg
bebob B290CINE 14.4/28.8V 294Wh3.35 lb / 1.52 kg
Anton/Bauer Dionic 26V Lithium-Ion Battery
(240Wh, B-Mount)
3 lb / 1.36 kg

How does this weight compare to the competition? Well, above you can see B-mount batteries with similar capacities. All of the available batteries have pretty similar weights.

It has physical dimensions of 15.4 x 10 x 8.7cm / 6.06 x 3.93 x 3.42″. The size suits the Alexa 35 reasonably well and the battery contours to the shape of the camera.

Build Quality

The Fxlion 293Wh 28.8V B-mount Battery Pack is solidly constructed.

I like the contoured ridges and indents on the sides of the battery because it makes it very easy to hold regardless of the weather conditions or when you are wearing gloves. This is the easiest to grip and hold onto the B-mount battery I have come across to date.

The locking mechanism is slightly different from other B-mount batteries that I have seen. Instead of pushing the release mechanism in, you slide it down to release the battery. Because B-mount batteries have the mount on the battery and not on the camera plate receptor, they can be designed in various different ways.

I do like the design of the release mechanism on the Fxlion as it is easier to remove the battery from the camera and chargers. By not having a push mechanism button the chance of holding onto the battery while operating and accidentally removing the battery is minimized.

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The only thing that slightly concerns me when it comes to build quality is that the release mechanism on the battery isn’t made out of aluminum. It looks to be a hard plastic material. Because B-mount actually has the mount on the battery itself, if this breaks, the battery will get stuck on your camera.

I like that the battery is equipped with rubber cover protection so if you do happen to drop it at least there is some protection.

Fxlion has used special materials when designing the battery so that it can bear a temperature of up to 230°C. This solves the issue of having high-temperatures damage components caused by high current discharge.

The BM-HV300 battery features built-in protection against over-heat, over-charge, over-discharge, and over-current.

Inputs & Outputs

The Fxlion 293Wh 28.8V B-mount Battery Pack features a 10.05Ah high capacity, and a 10A constant load at 250W.

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Early on, ARRI recognized a B-mount power issue (mainly because of the original LF) and recommended a minimum of 10A load for HV on B-mount. Since that time, ARRI has softened its stance on B-mount minimum specifications because they need B-mount adoption. The only slight concern with this is that if you don’t use a higher amperage pack, you may end up with a shorter service life for the battery packs since they could be continually overstrained depending on how you are using them. Luckily the Fxlion battery provides 10A.

It supports 20V/3A 60W(max.) fast charging via USB-C and it offers a good array of outputs.

As far as outputs are concerned this is what the battery has:

  • 2x D-Tap Outputs 16V/4A 64W (max.)
  • 1 x USB-A Output: 5V/2A 10W (max.)
  • 1x USB-C Output: 5V~20V/3A 60W(max.) / Input: 20V/3A

I did find it a little strange that the D-tap ports are located on the left-hand side of the battery. It would have made more sense to have placed them on the right-hand side as that keeps them out of the way of the operator.

Having a USB-C 60W input and output is really handy. It allows you to power a laptop or other device from your battery, or conversely, you can charge the battery through a Macbook power supply (although this is relatively slow).

Display Information

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The battery doesn’t feature an OLED display so you don’t have any way of seeing key information about the battery’s status. The only power indicator on the battery is a 5-stage LED. While I do like having a digital display on a battery, if the battery is clearly indicating its status in my EVF and LCD screen then it does somewhat negate the need for one.

The battery utilizes a smart communication system, that allows it to display the battery voltage /battery capacity /operating time/working current on the camera.

What cells does it use?

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A lot of the cells are manufactured by companies such as Sony, Samsung, and Sanyo. You also have manufacturers such as ANSMANN AG who make the cells for bebob. Regardless of who makes the cells, all cells are divided into three levels A, B, and C. The lower the rating, the cheaper the price and of course the worse the performance.

Very few companies selling batteries actually disclose what cells are being used in their batteries. I don’t know who makes the cells inside the Fxlion battery, but I do know that they are high-rated 18650 cells.

18650 cells are the most common cells used by most battery manufacturers. One of the exceptions to this is the Core SWX Helix MAX batteries that use the newer 20700 cell size. This is the reason why those batteries are wider and not taller than some other batteries. At least to my knowledge, the operational functionality of batteries using 20700 cells exceeds that of batteries using 18650 cells. In saying that, 18650 cells are more than up to the task of delivering enough power to cameras like the ALEXA 35.

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According to Fxlion, the cells are well protected inside the battery pack, and wireless bonding with PCB makes it simple and easy for it to be opened if it needs to be repaired.

It’s not flight safe

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The trouble with high-power draw cameras is when you come to travel. You can’t take any lithium-ion battery with a capacity above 160Wh on a commercial plane.

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With a capacity of 293Wh, this battery is going to have to stay at home if you fly a lot. This is something you need to clearly take into consideration when you are looking at batteries for the ALEXA 35.


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The Fxlion 293Wh 28.8V B-mount Battery offers a high capacity, has lots of outputs, and it is well-made. The battery is easy to grip and hold and I like that it has a USB-C input/output so you can use the battery to charge other devices as well as charge the battery without needing to carry around a large B-mount charger.

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The negative aspects of the battery are that there is no LCD display and that the D-tap outputs are on the left-hand side of the battery and not the right.

The ALEXA 35 balances really nicely on the shoulder and the Fxlion battery adds a nice amount of weight at the back of the camera, especially if you are using a larger lens. In saying that, all of the B-mount batteries I have tried to date work well when you want to shoulder mount the camera.

Price & Availability

The Fxlion BM-HV300 293Wh B-Mount Lithium-Ion Battery will be shipping shortly for $719 USD.

Fxlion BM-HV300 293Wh$719 USD
SWIT HB-A290B 290Wh 28.8V$789 USD
Core SWX Helix Max 275 Lithium-Ion
Dual-Voltage Battery
$825 USD
bebob B290CINE 14.4/28.8V 294Wh$975 USD
Anton/Bauer Dionic 26V Lithium-Ion Battery
(240Wh, B-Mount)
$1,025 USD

Above you can see how this price compares to the competition.


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The Fxlion BM-HV300 293Wh B-Mount Lithium-Ion Battery for ARRI ALEXA 35 is a solid offering and it is very competitively priced. To my knowledge, this is the most affordable 290Wh battery on the market.

It is easy to grip and hold, I like the release mechanism and the overall build quality, and it does the job without getting in your way. It is also nice that it has a USB-C input/output.

The negative aspects, as I mentioned in the review. are that this isn’t a dual voltage B-mount battery and the D-taps outputs should be on the other side of the battery. While I don’t mind the rubberized protection on the battery I wish it wasn’t a bold blue color and I would have preferred to have seen something more subtle, like grey or black.

While it is good to see more B-mount battery options starting to come to market, it will be interesting to see when or if other manufacturers start to release products that utilize B-mount.

Fxlion B-mount chargers

Fxlion makes two B-mount battery chargers. The FX-BM4LC 4 CH B-Mount Charger and the Fxlion Dual B-Mount Battery Charger ($399 USD).

The 4 CH B-Mount Charger as its name suggests, is a four-channel charger that is capable of charging, you guessed it, four B-mount batteries at once. The charger can provide 4 Amps charging current simultaneously to all channels. This basically means you can charge your batteries fairly quickly. Charging works simultaneously for all channels. The charger also features a built-in ventilator that makes sure the charger doesn’t overheat in high ambient temperatures. Other safety features include a built-in protection-circuit with over-current, over-voltage, and short-circuit protection.

There is also a top carry handle which is always a handy addition to have. The charger weighs 56.61 lb / 3 kg. This weight is ok for a four-bay charger.

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The Fxlion Dual B-Mount Battery Charger is a compact, tabletop-style charger for two 26V B-Mount batteries. It is compatible with standard B-Mount batteries, and you can simultaneously charge to batteries at 2A per channel. Additional features include SMBus communication, automatic voltage detection, and two status LEDs.

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