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.





Batteries and output:

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.


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).

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.







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.

reserved for updates...

Nice man, I'm loving that intergrating sphere, how'd you make it?

firelord777 said:

Nice man, I'm loving that intergrating sphere, how'd you make it?

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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).

Nice review so far. Thanks. Will you be adding beamshots too?

subwoofer said:

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.

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This has me worried a bit. What happens after the 36+42 mins of turbo, will the light be totally drained or will it scale down to a lower setting and continue running? (in other words should I interpret the flat line at 100 lumens as "yes it will still work as low light"?) And did you do a run with the AA pack on the BT-20? I'm sort of curious on how long it will run, it's sad that the low-battery warning comes immediately on but it doesn't tell me how long it runs (if at all)
One of the interesting things about this light to me is the fact that it can handle both power sources, but now you only done AA with BT10 and 18650 with BT20, where you specifically mention that either light can work with either source.
Anyway loving the input so far, thanks for the review!

rockhopper said:

Nice review so far. Thanks. Will you be adding beamshots too?

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Very unlikely due to time constraints and that this is a 'Performance Review' So is only showing the technical performance and beamshots don't come into this.

rockhopper said:

What happens after the 36+42 mins of turbo, will the light be totally drained or will it scale down to a lower setting and continue running? (in other words should I interpret the flat line at 100 lumens as "yes it will still work as low light"?)

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The runtime trace shows exactly that. It does drop to 100lm for just over 10mins before the protection kicks in and cuts the output completely. The BT10 just fades and fades and fade, so no surprise darkness.

rockhopper said:

And did you do a run with the AA pack on the BT-20? I'm sort of curious on how long it will run, it's sad that the low-battery warning comes immediately on but it doesn't tell me how long it runs (if at all)
One of the interesting things about this light to me is the fact that it can handle both power sources, but now you only done AA with BT10 and 18650 with BT20, where you specifically mention that either light can work with either source.

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Again due to time constraints (I do this voluntarily in my own time) I have not logged the runtime of the BT20 running on the AA pack nor the BT10 running on the 18650 pack. If you bought either one you would only have the matching pack. I just happened to decide to buy both as I always cycle with at least two lights and wanted the performance of the BT20 with the reliability of the BT10 not leaving you in the dark as running on AAs means there is no protection circuit to trip.

Ok, very clear answers. I can understand the lack of time, the review you given so far has been very helpful! I was just curious if you were going to add more (seeing a reserved post and all) but I can totally relate to being too busy to bother with it. I dont see myself running the turbo a lot, from what I've read so far medium and high are very bright already, and half my normal cycle route is in well lit city area where 'low' probably is too much already. (well enough never is enough :candle So I was wondering a bit about other runtimes but I think the max-runtime will give a good impression on the max. It's a shame that the warning light is kinda useless. Maybe Fenix will bring out the BT30 with improvements, though it seems cancelled. I was hoping they would continue developing bike-lights.
Thanks for the replies, much appreciated.

http://dx.com/p/1298a-12-6v-9800mah-rechargeable-li-ion-battery-w-us-plug-power-adapter-227814 Do you thinl it will run on one of these?

DavidAD said:

http://dx.com/p/1298a-12-6v-9800mah-rechargeable-li-ion-battery-w-us-plug-power-adapter-227814 Do you thinl it will run on one of these?

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If the connectors are compatible, theoretically it should.

Personally when you have a pack taking two 18650s included with the light I would not bother with trying something like this.

subwoofer said:

If the connectors are compatible, theoretically it should.

Personally when you have a pack taking two 18650s included with the light I would not bother with trying something like this.

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I got highest capacity 4 18650 pack with a dx bike/headlamp, which barely last 4 hours. It is better to bring your own named brand cells to the fight, as the generics you may get 700 milliamp hours. I seem to get over 4 hours at the 464 lumen setting on only two Nitecore 2300s. More than I would expect, but I am asking no questions.

Got BT20 in the spring of 2013. In short, I consider this a landmark light in my large search for the perfect lighting. I have used it for scores of apartment touch-up jobs, where you only wish put exactly as much paint on a wall/apartment as quickly as is needed. It has allowed me to walk circles around hard head that insist on sunlight light or fixed lights.

The color is excellent for an xm-l/okay, compared to an xp-g. I bought it for the 300 lumen setting, but found the lux too weak at 300 to work by; so, I use the 450 (464) lumen setting (4k candela, roughly) which illuminates a 5-7 foot by 5-7 area reliably for about 4 hours. 4 hours is bottom of acceptable runtime; I find acceptable for this limited application (a sprinting race, if you will). The beam pattern is about as wide as it gets and still maintain roughly 4 hours at 4k class candela. Compared with other bike lights: if you want a strong but floody (max flood for throw/runtime allowable), this is the light. And the color rendering is a plus.

The HUUUUGGGE drawback of the light is that mounting on headband, it is barely tolerable (intolerable to the hourly workers) to me. And, the cord is barely long enough; the cord is not curly (which always worked well in telephones of the 20th century. A replaceable, sacrificial cord would be nice too, in theory.).

I can imagine buying a cheap comfortable bike china direct light with the large crown. Ripping the head & battery pack off and mounting the bt20 up. Not sure how I would deal with the hinge.

I think, if Fenix fixed the form factor, the light may catch on as a worklight.

degarb said:

I got highest capacity 4 18650 pack with a dx bike/headlamp, which barely last 4 hours. It is better to bring your own named brand cells to the fight, as the generics you may get 700 milliamp hours. I seem to get over 4 hours at the 464 lumen setting on only two Nitecore 2300s. More than I would expect, but I am asking no questions.

I can imagine buying a cheap comfortable bike china direct light with the large crown. Ripping the head & battery pack off and mounting the bt20 up. Not sure how I would deal with the hinge.

I think, if Fenix fixed the form factor, the light may catch on as a worklight.

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Good point on the cord, I find it a bit stiff and can slam against my bike if I attach it in a hurry. But with the extention it runs from the front to rear of my bike with room to spare, are you that tall that you still find it short? I love the neutral color on it as well. Though I strictly use it as a bike light. I also love the ease to adjust the light either up/down or left/right, great to light up animals in the dark that run off.

As for a worklight, maybe the newly announced HP30 ticks the boxes? It's going to run on 2x18650 and has 500 Lumen as high setting, with a bonus "boost" of 900 while you press a button.

Thanks for heads up on the hp30. If the 200 lumen mode gets 9 hours and over 4k candela, we should have a winner. Especially, if the 400 lumen mode gets over 4 hours. I am guessing xpg2.

The external pack isn't as ballsy as the 2 18650 xml headlamps, now on some direct from china sites. This external form factor is good for full day jobs. But probably would not be first choice (as the rear mounted pack) for end of day (and morning) light.

I do not think it can be emphasized enough the need to use protected cells in a remotely mounted 18650 pack. I have already had one cord short, where the protection kicked in and saved me a fire. Also, a name brand, so you can trust the protection.


Fenix also could be ahead of others by adding a fuse in the battery compartment...In the hp30 you have a usb charger, so I wonder if, in the battery compartment, the do not include a current fuse, as well as over & under charge protection. Heeerrrres, hoping.

My beamshots of the bt20 against hp11, hp25, lowes xpg, etc.
https://googledrive.com/host/0ByvnKHNhvrTmYm1IOHNfUEttYmM/

Thanks for those images degarb. I notice that the HP25 has quite a "gap" in "full monty" mode (i presume that means spot & flood combined). Quite disappointing, glad I didnt order that one already. Guess for me it's between HP15 and the 30, once it arrives. The TK35 looks like a winner but I like the wider flood of the BT20 better, I'm curious why you included the TK35 (because I didnt think it can be headmounted, right?) btw.
All in all the BT20 is a great light for me, I wonder if you can interchange the battery compartments (external packs) between the different Fenix lights (like BT20 and the BT10, HP15 and HP30) Anyone tested that out yet?

rockhopper said:

Thanks for those images degarb. I notice that the HP25 has quite a "gap" in "full monty" mode (i presume that means spot & flood combined). Quite disappointing, glad I didnt order that one already.

Guess for me it's between HP15 and the 30, once it arrives. The TK35 looks like a winner but I like the wider flood of the BT20 better, I'm curious why you included the TK35 (because I didnt think it can be headmounted, right?) btw.
All in all the BT20 is a great light for me, I wonder if you can interchange the battery compartments (external packs) between the different Fenix lights (like BT20 and the BT10, HP15 and HP30) Anyone tested that out yet?

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You should only expect peripheral vision with the hp25 up close (via its very low candela flood side). The hp25's biggest strength is the 1. flood side (great runtime and optical advantage over a naked led) and 2. handy, easily accessible spot when needed 3. Drive level on spot makes sense if you modify battery pack to two 18650 (though more tunnel vision than xpg or xml with same lux) 4. the dual head is just way cool.

I tend to make my own headlamps from dropins or flashlights, when I get disgusted with pace of headlamps to keep up with annual changes in technology. The tk35 could easily be modded to a headlamp, since the head unscrews. Also, if someone had the tk35 (or its 8 aa equivalent, tk41?) the comparison is useful. Also, I use the tk35 as a wristlight (oh, mama, making that one work.). I love the tk35's 360 mode, as it is a long runtime that clearly stomps the visual acuity of most other lights. Though, I think-for painting touchup- the bt20 is a better balance of flood, hotspot size, and punch at 450 lumen (unfortunately, though, too short runtime for daily usage when not touching up), as a headlamp, than the tk35.

If the hp30 runtimes overlay well with a workday, and the led were an xpg2 S2, I may have to buy one. I do not own an xpg2 s2, part of me says: "must buy xpg2 s2, asap." As it seems , http://www.fenix-store.com/fenix-hp30-led-headlamp-grey/ ,they use and xpg2 r5 (Old news, and I already have purchased 5 xpg r5's over last year).

Anyone know if the BA4A battery pack can be bought separately. Seems like a good option for quick battery changes in the field:thumbsup:

Illum said:

Anyone know if the BA4A battery pack can be bought separately. Seems like a good option for quick battery changes in the field:thumbsup:

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When Fenix released these bike lights, it was listed as a optional accessories. But I've never seen it anywhere, in stock.

My BT20 pack broke and myfenix.co.uk had replacements, but I had to ask. It wasn't listed as an item on the webiste. It might be worth checking with your local official Fenix distributor/supplier to see if they can get it for you.