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  1. #1
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    Fenix BT10 / BT20 Bicycle Light Performance review (4xAA, 2x18650/4xCR123)

    Rather than a full in-depth review, this is a brief 'Performance Review' of the Fenix BT10 and BT20 bicycle lights.

    I have run the lights through the same technical testing I normally carry out for a full review, and am presenting the results in a more concise way so you can easily see how they actually perform.



    The BT10 and BT20 can comfortably be mounted on a helmet as well as handlebars.





    [SIZE="5"]Batteries and output:[/SIZE]

    The BT10 uses a 4xAA battery pack and the BT20 a 2x18650/4xCR123 pack. Either pack can be used with either light, but when using the BT10's pack with the BT20, the low battery light shows straight away.

    The BT10's battery pack



    The BT20's battery pack



    One slight disappointment is the low battery warning, which does not help much. The BT10's switch stayed green all the way down to a very dim output. The BT20's switch went red after 36mins of Turbo, but then continued to output the Turbo level for a further 42mins with the low battery warning.


    [SIZE="2"]To measure actual output, I built an integrating sphere. See here for more detail. The sensor registers visible light only (so Infra-Red and Ultra-Violet will not be measured).[/SIZE]

    Please note, all quoted lumen figures are from a DIY integrating sphere, and according to ANSI standards. Although every effort is made to give as accurate a result as possible, they should be taken as an estimate only. The results can be used to compare outputs in this review and others I have published.

    The BT20 on test.



    Fenix BT10 4xAA Eneloop I.S. measured ANSI output Lumens PWM frequency (Hz) or Strobe frequency
    Turbo 369 0
    High 219 0
    Low 83 0
    Strobe Not measured 6.8 and 1 mixed


    Fenix BT20 2xARB-L2 I.S. measured ANSI output Lumens PWM frequency (Hz) or Strobe frequency
    Turbo 763 0
    High 464 0
    Med 306 0
    Low 104 0
    Strobe Not measured 6.8 and 1 mixed


    These lights utilises an electronic switch, so there is parasitic drain to consider.

    BT10 – 0.5uA – 165 years to drain batteries
    BT20 – 1.8uA – 456 years to drain batteries

    The runtime graph shows the output traces for both the BT10 and BT20 running on maximum output and with a cooling fan.





    Test sample provided by Subwoofer for use on my night time bike rides.
    Subwoofer - Objective and Honest reviews
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  2. #2
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    reserved for updates...
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  3. #3
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    SW, glad you are doing another review on the BT20. Love your work as usual. I've been looking out for more information on the BT20 since it was mentioned to me that day. I particularly like how the BT20 lumen reading flatlines at the 10 minute point and maintains consistent brightness all the way to battery depletion. Can you explain at which point in time you determine the lumen rating of 763 on Turbo mode? 1 minute? What is the actual reading between 10 min and beyond? Also, are you able to say if brightness is improved if you used better cells?
    Leonard - All things Xeccon + Beyond
    mtbRevolution.com

  4. #4
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    Quote Originally Posted by mtbRevolution View Post
    SW, glad you are doing another review on the BT20. Love your work as usual. I've been looking out for more information on the BT20 since it was mentioned to me that day. I particularly like how the BT20 lumen reading flatlines at the 10 minute point and maintains consistent brightness all the way to battery depletion. Can you explain at which point in time you determine the lumen rating of 763 on Turbo mode? 1 minute? What is the actual reading between 10 min and beyond? Also, are you able to say if brightness is improved if you used better cells?
    The lumen ratings I quote are according to ANSI specifications (or as close as I can get). This means the reading is taken 30s after turning on. I actually log the output from turn on and can then easily see what the output was at the exact 30s time stamp.

    Once the output goes completely flat, it has settled at 722lm (after around 16mins).

    The Fenix ARB-L2 cells used for this test have only a few cycles on them and are excellent performers. From past experience I would not expect any significant change in output level with different cells, instead only a change in runtime. Unfortunately I don't think I'll have time to re-run the tests with different cells to confirm if my suspicions are true.
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  5. #5
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    Quote Originally Posted by subwoofer View Post
    The Fenix ARB-L2 cells used for this test have only a few cycles on them and are excellent performers. From past experience I would not expect any significant change in output level with different cells, instead only a change in runtime.
    I'll confirm this as I ran a test with some cheap DX batteries and another test with some Panasonics 3100ma. The Panasonics had longer run times but was not any brighter, at least with my eyes!
    "By Your Command"

  6. #6
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    Great review. I've just received my fenix B20 and wow. I'm blown away. I have been using alleged 1200 lumen ebay copies, which don't get me wrong are great for the money, but not reliable. I've had a couple and the battery packs fail. Wish I spent the extra coin in the first place and got a B20. Everything from the build quality, to run times, to looks. It's all there. Was amazed at the spill from the reflector, the dual spot which not only lights up the ground in front but also the front well into the distance. It's supposed to be 750 lumens, and it's easily as bright as my 1200lumen flea bay special. It's awesome. Do I sound like I'm impressed lol. Seriously though, the build quality of the whole thing, you know it isn't going to let you down. This is my fourth fenix , and I've always been impressed, probably wouldn't buy anything else now.

  7. #7
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    The 2014 MTBR lights shootout mentions that they plan to test the Fenix BTR20 during round 2. Curious how the BTR20 compares to the BT20.

  8. #8
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    I'm amazed how little you see written about the b20 as for the btr ? Really ?

  9. #9
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    Well I've scoured the net, and apart from a mention in a test on here if can find nothing else about it. Not even a picture. In the chart it doesn't get mentioned either. Myth ?

  10. #10
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    Yeah, you don't hear much which is why I'm looking forward to the MTBR review on the BTR20. I've mostly gone off Amazon reviews. I already have a Fenix PD32UE + batteries/charger so I'm thinking that on my helmet + the BT20/BTR20 might be the perfect combo. Will also be cheaper to buy extra 18650's vs an extra proprietary battery pack that most companies use.

  11. #11
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    you cant go wrong with fenix. i have an EO1, TK1O, PD30, B20, AND father christmas is getting me a PD35 850 lumen light sabre because ive been a very very good boy lol

  12. #12
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    Quote Originally Posted by crazee horse View Post
    ...AND father christmas is getting me a PD35 850 lumen light sabre because ive been a very very good boy lol
    LOL! It pays to be good....

  13. #13
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    Still struggling to find any links ?

  14. #14
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    I generally ride with the Cygolight 380 flood on my bars and a Jet 850 lumen spot on my helmet. Plenty of light for most of our local trails. I picked up a BT-10 for a fair price. The light output is comparable to my Cygolight 380. The beam spread however is much more of a spot than a flood. The main reason I picked it up however is that it is a quality light with replaceable AA batteries. I am planning to do more bikepacking in areas without a way to recharge my regular trail lights. Being able to carry or buy AA's along the trip is going to be great.

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    can the BT20 run off regular AA batteries on the web site it only indicates the BT10 also does anyone know what the run times on AA batteries? Thanks for the write up

  16. #16
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    Quote Originally Posted by jharness View Post
    can the BT20 run off regular AA batteries on the web site it only indicates the BT10 also does anyone know what the run times on AA batteries? Thanks for the write up
    Regular AA alkaline batteries can't deliver the current needed to run the BT20. (there marginal for the BT10)
    If you use AA Nimh or Nicd it would do ok.
    Jim Harger
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  17. #17
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    Great review!!! Are you a member over on CandlePower Forums? If not, you would make a great addition.

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    I just bought the BT10 for my first Brevet, the Santee 400k, based on this and other reviews. This involved over 12 hrs riding in the dark, over decent roads in SoCal. I wanted AA power and light weight and reliability. Observations:

    The color of the light beam is good for seeing at night. This is more important than you might think. Some led light colors don't work very well. I have several cheap chinese led lights for night mtb rides. Pink or green hues tend to wash out features.

    I got 9 1/2 hours of useable light out of one set of Tenegy lithium primary AA's. I think that's pretty good duration. This was a combination of low power for slower climbing speeds, medium power (200 lumen) up to 20mph, and brief periods on turbo for fast downhills. I wanted more light than turbo at 40mph, my fastest speed. That's pretty fast for night riding, and I could have just slowed down, but I'd been riding for 23 hrs and I wanted to finish before I fell asleep!

    The dual beam feature maybe helps a little. The inner part of the reflector is OP which helps to spread the beam nicely. I aimed for 15 to 25 ft. in front and had a wide spot and good fill, with a dim spot right in front from a prismatic feature on the top part of the lens.

    I'm very happy with this light. It's higher quality than my other lights, and I expect to get many years of service. For off road I would definitely want more light, perhaps the BT20. For riding at a steady pace on good roads, this one fits the bill. It's worth the retail price (I found it online for half). It's been out for a while and prices should continue to fall.

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