# User review Fenix BT20



## pucked up (Mar 22, 2006)

I was chosen to review the new Fenix BT20 from a list of applicants that applied back in October 2012. *This product was sent to me free of charge and I have no direct affiliations with this company.*

My objectives for this test will be to provide my option on:
1 - Quality of the components
2 - Run times
3 - Beam patterns and its usefulness on the trail.

This will be an ongoing review as I have not yet been able to make time to ride with this light. But since receiving the Fenix BT20 only three days ago, I have been out to shoot some beam shots on one of my favorite trails. I was quite surprise on the results.
But first some pictures of what's included in Fenix's BT20 "The World's First Bike Light with Dual Distance Beams."

























Side view








Back








Top








With battery case








Front









The components that are included in the box are, user manual, warranty card, helmet strap, extension cable, three O-rings, battery case and battery case holder.

*Oh&#8230;Batteries are not included!*

The user manual came in English and Chinese. It's pretty straight forward, gave good descriptions on the products features, parts included, technical info on battery to use and run times. Also has instructions on mounting and operation of the light. As well as the all-important safety tips with diagrams to along with certain sections.

Warranty period is 24 months and Fenix will repair any defective product for free.









The helmet strap is made from plastic with nylon straps and a plastic push down clamp. I would of preferred Velcro strap instead as the push down clamp seem kind of thin. The mount has a foam bottom to prevent it from moving once clamp down to your helmet. As for this type of mount, the height of the light is about the same as most other brands out there. I guess this is an issue companies have when they want their lights mounted both on the handle bars and on the helmets.









The extension cable is stiffer than I would like. It's only 70 cm / 27.5 inches in length, while most other companies have their extension cable at the 1 meter mark (about 39 inches). So this extension cable falls a little short, especially if you're a tall person.









Battery case holder is made from plastic has a screw down lid and holds two 18650 or four CR123A lithium batteries. The holder fits in a nylon pouch which you can attach via Velcro to the back of your helmet, bike frame or just put it in your water pack pocket. My dilemma is, it only holds two 18650's. Why? There is no option to use four 18650 for longer run times. To me this is a deal breaker, as I would like to have longer run times with my lights without having to change them while on the trail. The holder itself appears to be of quality. Opening the case, you'll see it has a washer around the top making this water resistant if not proof when screwed down tight. The case can only be closed one way and has markings on how the two pieces should come together. So there is no worries in reversing the terminals.









You get three O-rings, small, medium and large. Small and medium would be used the most. Medium mounts the light to the helmet strap. Depending on the type on handle bar you have, you'll either use the small or medium O-rings. I found the small O-ring gave me a tighter grip on my handle bars. The O-rings are about middle of the pack, it's not the thinnest and not the thickest that I've seen.









The light head is about 67mm in length, 38mm wide and 39mm in height not including the stand. Made out of aluminum, it's light weight and compact. It uses a reflector and has a glass lens. As you can see from the picture, the lens itself has an engrave etching on it at the top. Now this could be what gives the Fenix BT20 the dual beam pattern, which is what I'm guessing at. The light head has no openings, seem to be water resistant and can swivel 360 degrees to help with mounting.

The power button at the top of the light is made from rubber/silicone. Hold it about one second to turn it on and each press after will cycle through the four modes, low, mid, high and turbo. I love this feature as the flashing mode is not included in the cycle. To access the flashing mode you'll have to double press the power button. To return the normal press the power button once. The light also has memory, so it will remember the last mode you're in when you turn it off (except flash).

The power button is also an indicator of the battery capacity.
100% - 50% - Solid Green.
50% -20% - Solid Red.
Less than 20% blinks red.

I love this feature also. I always wanted to include this in my light build, but I'm just to lazy!

Light modes and run time are as follows:
Low - 100 lumens, 21 hrs run time.
Mid - 300 Lumens, 6.5hrs run time.
High - 450 lumens, 4hr run time.
Turbo - 750 lumens, 2hr run time.
Flash - 300 lumens, 21+hrs run time.

Now I did have an issue with run times. I ran a test for "Turbo Mode" to see if the 2hr run time was accurate and ran the test in front of a fan on mid setting. Batteries were fresh out of the charger. Both had a voltage of 4.1v according to my multimeter.

Place both in the holder and took voltage reading again.
No load - 8.0v
Low - 7.9v
Mid - 7.8v
High - 7.5v
Turbo - 7.1v

Now to my surprise, after about 2-3mins the battery indicator went red on the power button. WTF? I let the test continue and after about 40mins the light automatically switches from Turbo to High mode. I would manually switch it back to Turbo but after about 5mins would switch back to High. At about the 1hr and 15min mark, the light drop to Mid. At about the 1hr and 35min mark drop to Low. At this point the power indicator was a solid red. I can manually switch to Turbo mode but the light would automatically cycle it down to low mode. At the two hour mark the light was at "Low mode" with a solid red indicator.

I stop the test at this point. Re-did the test with a new set of fresh batteries and got the same results as above. I don't know why this has happened, was it the light or my batteries? I have about eight blue TrustFire 18650 from DX. I know they're not the best, but I haven't had any issue using them on my light builds. So what gives? I've sent an email to Bob at Fenix regarding this issue and waiting to hear back from them. Or maybe they'll come on hear with an answer. Stay tune for an update. This is a major concern for me and anyone looking into buying this product. My option is&#8230;four 18650s is better than two. Would it cost any more to make a holder for four 18650s as batteries are not included with this set?

Another concern is that Fenix has reversed the power plugs. The male end of the plug is now on the battery and the female part is on the light. Not sure if this was indented to deter using existing battery packs that you may have. Or how safe it is to have the male metal plug on the battery end? Will having this on the battery make it easier for them to short out?

Also it would be nice to know what the max input voltage is. Maybe Fenix should include this in their manual under "Safety Tips" just in case anyone is trying to use a DIY battery pack. So that they don't short out the light.

Now to the good part&#8230;beam shots!

Before I show you the pictures, I have to say that I was very impressed with the amount of light and the beam patterns the Fenix BT20 produces. It does give you the best of both worlds. If I have to ride with one light and one light only, the Fenix BT20 would be at the top of my list. Hands down this would be my choice for a handle bar light. Not sure about a helmet light just yet, I guess I have to ride with it to be sure. But I'm sure that having two Fenix BT20s will be all the light you'll need for riding your favorite trails at night. Unfortunately Fenix was not able to provide me with a second light to cement my option.

The LED used is an XM-L T6. My understanding that it has a neutral tint to it. I compared it to my neutral set up and the BT20 is more on the coolish side of things. I would say just below the 5000k mark.

So instead of using another thousand words, I'll let the picture tell the story.

Camera settings: Nikon D70s
Manual
ISO - 200
WB - Daylight
Shutter - 3 second
F stop - f4

Control No Lights









Low









Mid









High









Turbo









As you can see, to me you have a very useful beam pattern. A lot of light in-front of the bike and a good amount of throw so that you can see what is up ahead. My estimate is the amount of light thrown forward is usable to about 80ft. Having a second light should improve on this.

Comparing the beam pattern to my lights and that of my friends, I would need two lights to produces the same pattern. A wide flood on the handle bars and a tight spot on my helmet. The Fenix BT20 does both with one light set up pretty darn well!

I'll update this review after I have a chance to ride with the BT20. Posting more pictures and maybe a video.

*Update*


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## GSJ1973 (May 8, 2011)

Wow, TURBO mode looks sick! Great review, thanks for the detailed post.


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## colleen c (May 28, 2011)

Thanks for the review.

The 7.1 initial volt on start up in turbo mode is most likely an indicator that the battery is sagging under the load. I would think that if the setup was to use two cell , then higher quality battery like Panasonic NCR will keep the voltage in the 7.4 nominal range better and helps prevent the premature cutdown from Turbo to High mode.

Is there any protection circuit on the battery holder? Or do you have to use protected 18650?

I am interested in the dual beam pattern. Can you take a white wall beam shot at a distant where it will show the dual beam pattern? That may give us a better ideal of the beam shape pattern. Thanks


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## irv_usc (Mar 16, 2011)

As far as the battery holder, I was under the assumption that there was a 4-cell case available.

Is the mount removable if we wanted to change to a cateye or similar mounting solution?


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## derekbob (May 4, 2005)

This light looks like it would be awesome if they had just switched the connectors on the battery and lighthead. Any light manufacturer that uses a unique battery connection is shooting themselves in the foot if they want my business.


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## pucked up (Mar 22, 2006)

colleen c said:


> Thanks for the review.
> 
> The 7.1 initial volt on start up in turbo mode is most likely an indicator that the battery is sagging under the load. I would think that if the setup was to use two cell , then higher quality battery like Panasonic NCR will keep the voltage in the 7.4 nominal range better and helps prevent the premature cutdown from Turbo to High mode.
> 
> ...


If that is the case regarding the batteries, then people looking to get this product with their own non name brand batteries will be in for a rude awakening! An added cost for people waiting to buy this.

As to the PCB on the battery holder there is no info in the manual I assume there would be as it has memory and overheating protection. I was using protected 18650s. The green underside of the battery holders top is what I assume to be the PCB.









Here is a picture of the beam shot on a white wall taken about 9ft away. Sorry that's about as distance it's gonna get. White walls are limited in my home. As you can see, there is another spot just below the hot spot. My guess is, this is what gives you that flood in front of the bike. You have like a figure 8 in the center.


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## pucked up (Mar 22, 2006)

irv_usc said:


> As far as the battery holder, I was under the assumption that there was a 4-cell case available.
> 
> Is the mount removable if we wanted to change to a cateye or similar mounting solution?


The 4 cell case is for AA batteries only and did not come with the test package. I'm not familiar with the cateye mounts, but the battery sleeve is removable via Velcro straps.


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## pucked up (Mar 22, 2006)

If nothing comes up tonight, I may be able to take the BT20 out for a quick spin. The light and battery pack mounted on my helmet. It's well balanced, the battery not too heavy, it just feels weird. I guess I'm not the mount the battery to my helmet type of rider.


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## irv_usc (Mar 16, 2011)

pucked up said:


> The 4 cell case is for AA batteries only and did not come with the test package. I'm not familiar with the cateye mounts, but the battery sleeve is removable via Velcro straps.


Right, I remembered wrong about the battery case.

My second thought was whether the mount on the bottom of the light is easily removable?


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## Vancbiker (May 25, 2005)

The beamshot looks good with a nice crisp cut off to the sides. The helmet mount is bad IMO. Way too high off the helmet crown.


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## Cat-man-do (May 16, 2004)

So far nice review. Am I right to assume that the complete light head is made out of aluminum? Looks like this is using a two cell holder. Not great for long rides but if you conserve power by using high and mid level you should do well. I think this light is basically designed with commuting in mind and would likely work best on the bars.

I like the look and function of this lamp. I think it should do well as a commuter light.
Like Colleen said, better to use this with the a good set of batteries. Yes, buying a set of Panasonic 3100mAh cells or 3400 cells might cost a bit but well worth the money. The fact that this light powers down automatically is a nice feature because it will keep you from being caught without light for a longer period. However, expect this feature not to work so well in cold weather or with old batteries.


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## pucked up (Mar 22, 2006)

irv_usc said:


> My second thought was whether the mount on the bottom of the light is easily removable?


It should be, it's held on by one screw.


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## pucked up (Mar 22, 2006)

Cat-man-do said:


> So far nice review. Am I right to assume that the complete light head is made out of aluminum?


From what I can feel, I assume it's all aluminum. But I'm no metal expert.

I feel even with the best batteries you may only have about 1.5hrs run time on Turbo. A little short for even my low standards.


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## Nitro26 (Nov 6, 2012)

Looks like a good light


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## PatrikL (Nov 21, 2010)

pucked up said:


> I have about eight blue TrustFire 18650 from DX. I know they're not the best, but I haven't had any issue using them on my light builds. So what gives? I've sent an email to Bob at Fenix regarding this issue and waiting to hear back from them. Or maybe they'll come on hear with an answer. Stay tune for an update. This is a major concern for me and anyone looking into buying this product. My option is&#8230;four 18650s is better than two. Would it cost any more to make a holder for four 18650s as batteries are not included with this set?


Some blue TrustFire batteries have had problems with protection PCB. And they usually degrade significantly with time, for example see

```
goo.gl/0u6KA
```
 .
I think that two batteries are enough, battery pack is light and compact. But do not use junk cells, go and buy something better...  Sanyo cells are very cheap, Panasonic mentioned before is good choice too. But they have different discharge curves and I am not sure what is better for this light. 

```
goo.gl/8mxko
goo.gl/QcXjv
```


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## Cat-man-do (May 16, 2004)

pucked up said:


> Light modes and run time are as follows:
> Low - 100 lumens, 21 hrs run time.
> Mid - 300 Lumens, 6.5hrs run time.
> High - 450 lumens, 4hr run time.
> ...


I think the listed run times are a little over the top. I would think if you ran the light on high (450 lumen ) you should get about 3-3.5hr depending on how good your batteries are. Of course you're still going to have to deal with the auto-power down feature at some point. If this light is using an XM-L emitter no way it will get 2hrs on turbo mode with a two cell battery.

The auto-power down feature is nice but a lamp like this is really not intended to be run on the turbo mode for more than a couple minutes. I think if you run the lamp on high most of the time you will likely be able to ride a couple hours before the auto-power stuff begins to kick in. If I was going to buy this light that is what I would be wondering.

pucked....*Can you start the lamp in high and then tell us when the auto-power down kicks in. * Also to be on the safe side make sure you have a fan blowing on the lamp. Dont won't to confuse the auto-power down with the thermal management circuits as both have the capability of powering down the lamp.


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## mdemm (Aug 4, 2010)

Very nice review pucked up... I am about ready to get a helmet mounted light myself. Pretty much narrowed it down to Xera, 808U, BT20. Been patiently awaiting the release of the Gloworm X1 before I make my decision. Was wondering if you are able do some side by side beam shots comparing the BT20 to another light ??? It would be interested to know how the BT20's performance would be like using Panasonic's 3100mAh or 3400mAh batteries ???


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## pucked up (Mar 22, 2006)

Cat-man-do said:


> If this light is using an XM-L emitter no way it will get 2hrs on turbo mode with a two cell battery..


That's what I was thinking. I'm guessing you'll need 3 cells minimum and I may have something that I can use for this light.

I was told by Fenix that the max voltage for this light is 12V. I'll keep you guys updated.



Cat-man-do said:


> pucked....*Can you start the lamp in high and then tell us when the auto-power down kicks in. * Also to be on the safe side make sure you have a fan blowing on the lamp. Dont won't to confuse the auto-power down with the thermal management circuits as both have the capability of powering down the lamp


This was going to be my next test. Hopefully sometime this week and yes I will have a fan blowing on the light which I had during the original test.


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## mattthemuppet (Jul 16, 2004)

those blue Ultrafires are sagging badly under load. You'd be able to use 4 of them (2S2P) easily enough, but 2 of them can't provide the current. I found this out with a light I built for a friend and ended up rebuilding the battery pack with Panasonic cells instead which worked just fine. I doubt that there's a PCB in that pack, but if you can unscrew it and take a picture of the other side we'd know for sure.

Other than the dated UI and the crazy high helmet mount, the buying your own batteries kills it for me from a value perspective. I forgot what the retail was ($110?) but adding a couple of decent cells is going to run to ~$20 give or take at which point you're heading into Gemini Xera territory, which looks like a far better light. Or save $30-40 and get a half decent Magicshine from a reputable reseller with higher ouput and longer runtime.

The dual beam thing looks like it works pretty well though.


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## colleen c (May 28, 2011)

2hr runtime from 2cells driving a XML is doable. Gemini gets 2hrs off of their 2600 mah 2cells pack when they had the Xera outfitted with T6 producing 800 lumens. You should be able to get close to 2hrs running off two cell if those cell can handle the load and rated 2900 mah or higher. 

I concur with Matthemuppet with the idea of looking behind the board on the battery holder. If indeed there is a PCB built in, then running protected 18650 just add more total resistant to the circuit and creating more sag. If there is no protection board, then a test with something like AW18650 or Redilast should be perform. Personally I feel Fenix should have provided the tester with whatever cell they used for testing to the reviewer in case of any doubts.


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## xcracer450 (Aug 21, 2011)

Agreed...and looking forward to a response from Fenix...I am really interested in getting one of these..


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## Maximus_XXIV (Jun 7, 2009)

For me, the cutoff beam adds value because I am primarily looking for a commuting light for use around lots of other cyclists and cars. A 4 cell pack would be nice too. I was hoping someone would have a review up. Nice job!

At this point, I am undecided on a purchase.


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## pucked up (Mar 22, 2006)

Fenix should of included some cells for this test, but I assume they wanted to find out how other batteries will hold up to this light. Unfortunately I do not have any quality 18650 cells. I do plan on purchasing some in the near future, but for this test all I have are the cheap DX cells.

I may have found a solution to my crappy cells. Don't know if this is what Fenix wanted, but I'm going a head anyways.










As you can see, I took the extension cable and spliced it into a spare 3 cell holder. I just wish the extension was longer and more flexible. Haven't tested them yet, but hoping to get around 3hrs run time on Turbo if the protection doesn't kick in.










The nice part, the battery pack still fits into the battery sleeve from Fenix!

Some data using 3 cells are:
No Load - 12.3v
Low - 12.3v
Mid - 12.2v
High - 12.0v
Turbo - 11.7v

As for the Fenix battery pack, I don't think it has a PCB on it. But I could be wrong.









Up next testing the 3 cell pack, but not tonight.


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## mattthemuppet (Jul 16, 2004)

I hope the driver is rated to >8.4V otherwise it won't last long - I know that Magicshine drivers (the standard for Chinese bike lights I guess) don't tolerate 12V well. The better way to test the light properly with those batteries is to make a 2S2P pack with 4 cells, which will halve the current draw per cell.

TBH, if I was in the market for a light like this I'd either go for an all-in-one light (commuter) or a semi-decent single LED light like the Xera. The Fenix might be better if you're a flashoholic with a bucketfull of quality 18650s lying around and *a decent charger* (Cat?!), but otherwise there are lots of better options for similar money. Understandable given that Fenix is a flashlight maker, but this isn't a flashlight


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## abhisheknath (Nov 7, 2012)

I bought the Fenix bt20 about a week and a half ago and just received this email:

"It is with great regret that we received an email from Fenix (the manufacturer) last night asking that we NOT ship the BT20 lights we had just gotten in and had already starting processing for shipping. Apparently, there is a slight issue with the light that causes the "low battery indicator" to come on when in Turbo Mode after just a few minutes. We are told this does not affect illumination or run time so I'm sure Fenix will resolve this issue quickly. In the meantime, we are going to refund your purchase price. If you paid by PayPal, your refund should show up quickly. If you paid by credit card, it takes 2-3 days for a credit to appear on your statement.

We do apologize and hope you will re-order once Fenix has resolved this issue. "


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## xcracer450 (Aug 21, 2011)

Well, that's a bummer. Can you recommend something around the same price range with similar capabilities? No thread jack intended (please message me)


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## socal_jack (Dec 30, 2008)

A pointless test for most people I would think as I doubt they would hack their gear up unless they also got it free. Note that there is a 4 AA-cell battery holder available on their site for this also.



pucked up said:


> Fenix should of included some cells for this test, but I assume they wanted to find out how other batteries will hold up to this light. Unfortunately I do not have any quality 18650 cells. I do plan on purchasing some in the near future, but for this test all I have are the cheap DX cells.
> 
> I may have found a solution to my crappy cells. Don't know if this is what Fenix wanted, but I'm going a head anyways.
> 
> Up next testing the 3 cell pack, but not tonight.


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## pucked up (Mar 22, 2006)

*Taking the Fenix BT20 for a Ride*

Okay so I took the BT20 out for it's first ride tonight. First impression are:

*On the Handle Bars:*
*Pros:*
1 - Quick to mount/un-mount both the battery pack and light head.
2 - Light head adjustable 360 degrees.
3 - Compact does not take a lot of room.
4 - Awesome light output both flood and throw.
5 - O-rings kept light head firm to the bars.
6 - I love the flood pattern from this light!

*Cons:*
1 - No remote switch.
2 - Light output could be brighter.
3 - Need high quality 18650's which is not included.
4 - As with the batteries, charger not included also.

Riding with the Fenix BT20 on my handle bars out on the trails is awesome as I assume it would be. There is a wide flood light in front of the bike and a good beam throwing the light out on to the trail. The flood pattern is wide enough to cover the width of most trails and extends about 4ft out. A narrower beam pushes the light out from that point on.

Having only one light source is not enough to really attack your favorite trail and I wished that more light was available from the BT20. I would recommend a good helmet light to be used with the BT20. A combination of a good spot helmet light and the BT20's beam pattern would be a killer combo on any trail. This would be my set up of choice when going out at night.

Fenix hit the bulls eye when it comes to the LED tint. To compare it, I have from Ledsupply a Neutral and Cool White LED for my light builds. The LED that Fenix uses falls in-between the ones I bought. It's brighter than the Neutral, but still illuminates a natural look on to the trail not washing it out like Cool LED tints tend to do. Hopefully if you do use a second light with the BT20 the light tints match up. My second light didn't match up, but it was not a big issue for me. Or you can just purchase two BT20s!

What makes this light great is that you can rotate the light head 360 degrees. This means that you can center the light out on to the trail by adjusting it side to side. As most of us will have the lights mounted off center on the handle bars.

_*On the Helmet:*_
*Pros:*
1 - Light weight.
2 - Both the helmet strap and light quick to mount.
3 - Great light output.
4 - O-rings kept the light firm to the helmet strap.

*Cons:*
1 - No remote switch.
2 - Light output could be brighter.
3 - Need high quality 18650's which is not included.
4 - As with the batteries, charger not included also.
5 - The flood pattern.
6 - Height of the BT20 on the helmet strap is too HIGH!!
7 - Extension cable is too short!

Riding with the BT20 on my helmet was not as exciting as on the handle bars. It's not bad, it's just different. With my helmet lights I'm use to a tight / spot beam pattern. The BT20 I notice more of a flood than what I'm use to. Maybe it'll take me some time to get use to it, but this would not be my first choice as a helmet light.

My experience is like driving you car at night on a straight roadway. You then turn your head from side to side and have you headlights follow your head as your turn it. I'm use to having my flood light stay straight ahead of me and having my spot light scan a head of me. Having a second flood light may reduce this weird sensation, but you'll still need a good spot/tight light. I was surprise that the lights I've build with a tight optics throws a litter better than the BT20.

I would say that the BT20 makes a better handle bar light than a helmet light.

*Final Words:*
Fenix BT20 is a great product. The light head and components that comes with it is well made and of quality. The dual beam pattern is surprisingly well accomplished. The tint of the light is perfect for the trails and on the road. This makes a great Christmas gift for any mountain biker who like to ride at night!

Some items Fenix should work on are, extension cable, it's too short! It should be at the 1 meter mark like other companies. Also the cable is too stiff and made it shorter as the bends didn't straighten out.

The helmet mount is too high, it can be cut down a bit by having a semi circle mount instead of a full circle.

Should recommend high quality name brand batteries instead of just stating what type to use (if not using the ones from Fenix). Also have an option for a four 18650 battery case.

Finally, having a remote switch for the BT20 would make it more attractive as you will not need to remove your hands form the handle bars (when mounted on the bars) when cycling through. Also helps when using the BT20 as a helmet light as it's higher than most other lights.


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## pucked up (Mar 22, 2006)

socal_jack said:


> A pointless test for most people I would think as I doubt they would hack their gear up unless they also got it free. Note that there is a 4 AA-cell battery holder available on their site for this also.


Yes, I know, but I really only hack the extension cable.


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## socal_jack (Dec 30, 2008)

Well the rest of the review was pretty good. I noticed on their page that they do offer it with Tenergy batteries etc for $129 (says they're out of Fenix branded batteries)



pucked up said:


> Yes, I know, but I really only hack the extension cable.


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## spankone (Aug 31, 2011)

abhisheknath said:


> I bought the Fenix bt20 about a week and a half ago and just received this email:
> 
> "It is with great regret that we received an email from Fenix (the manufacturer) last night asking that we NOT ship the BT20 lights we had just gotten in and had already starting processing for shipping. Apparently, there is a slight issue with the light that causes the "low battery indicator" to come on when in Turbo Mode after just a few minutes. We are told this does not affect illumination or run time so I'm sure Fenix will resolve this issue quickly. In the meantime, we are going to refund your purchase price. If you paid by PayPal, your refund should show up quickly. If you paid by credit card, it takes 2-3 days for a credit to appear on your statement.
> 
> We do apologize and hope you will re-order once Fenix has resolved this issue. "


I've noticed on my sample that on turbo it instantly goes to red. IMHO I would wait until they fix it.

I also made it on to the testing list I hope you don't mind if I jump in on this thread.

Here's a link to my video review.































































































































































Now my first impressions are good I would certainly recommend using it as a bar light. Although the flash modes aren't really suited for commuting. I think a 750Lumen flash-strobe mode would soon get you run off the road. But the beam pattern is useful on the bars the modes are we spaced and run times seem good.

But has a helmet light it's very much a different story. The strap and mounting is solid but it sits way to high. With both light and battery fitted to the helmet it's way to heavy. And if used on its own as a helmet light you get a very distracting secondary halo. This halo is visible on the bars but its not distracting. On your helmet it gives you a very odd tunnel vision effect.

What I highly recommend is that fenix produce a third light to the range specifically for helmet mounting a 1x18650 using the new xp-g2 with the option of plugging an optional secondary 18650 for extended run times.

So I've used it in the woods I'll be hitting the road with it tonight.  and by next Wednesday / Thursday I'll add the second part to my video review.

Sent from my iPhone using Tapatalk


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## Cat-man-do (May 16, 2004)

pucked up said:


> That's what I was thinking. I'm guessing you'll need 3 cells minimum and I may have something that I can use for this light.
> 
> *I was told by Fenix that the max voltage for this light is 12V. I'll keep you guys updated.*
> 
> .


This might be why the auto-power down feature is not working as planned. It could be the driver was designed with too wide a voltage input range and the power kick-back settings are adjusted for the potential larger voltage. If the 3-cell set-up eliminates the quick indicator switch over than I am correct in my assumption.

If I'm right, Fenix will either need a new driver with a 8.4 volt max input or design the driver with a manual switch so that the user can set the driver for the right input voltage level.

It figures a torch manufacture would do something like this because many torches are designed the same way. Need I say, I've never been fan of torches ( or drop-ins ) that use the wider voltage range on their drivers. That's because when you power these drivers with a lower voltage battery ( say with a single cell 4.2volt peak 18650 ) but the driver can handle a 8.2 volt battery, there is always a significant drop in output once the single cell starts to discharge. This is why when I recommend torches or drop-in's I always tell people to get the ones with a max input of 4.2 volts ( if they are going to use a single cell 18650 lamp ).


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## spankone (Aug 31, 2011)

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## Wolfsburgfan (Jul 28, 2012)

I want one, the throw looks nice. Should I wait now given the problem?


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## Wolfsburgfan (Jul 28, 2012)

Any other light in this price range that I should look at? I want it mainly as a second light.


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## pucked up (Mar 22, 2006)

spankone said:


> I also made it on to the testing list I hope you don't mind if I jump in on this thread.


Not at all. You're welcome to post your result here.

It you have high quality name brand 18650s try and do the run time test on Turbo. I tried but my batteries were not up to par for the test.



Cat-man-do said:


> If the 3-cell set-up eliminates the quick indicator switch over than I am correct in my assumption.


Well, you're correct. I ran a test on Turbo mode with the 3 cell pack last night and the light indicator did not switch to red after 2-3mins. But after about 40mins it drop to High mode with the indicator still green. I had a fan blowing on it on high, it was warmish at best, so it's either that the heat protection kicked in or there is not enough juice with the batteries I used.

Testing HIgh mode with the original 2 cell battery pack the BT20 came with. I'll post an update later.

*Update:* The test on *HIgh mode* lasted for only *2.5hrs* then drop to *Low mode* and could no longer cycle to the other modes. The battery indicator light turned red after 40mins while on High mode. But Fenix did admit that they have an issue with the indicator light and I also wonder if they have and issue with the driver they used as Cat has said above.


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## Vancbiker (May 25, 2005)

I have a hard time understanding how the battery voltage sensing would work right at all if you raise the input voltage to 12.6 using a 3S battery. The end of useful charge in that battery will be ~9V. That's higher than the starting voltage 8.4V of the original pack. I'm guessing the driver is programmed to change the indicator color or light output at set values. Maybe it senses the voltage when first turned on and that selects values based on the starting voltage. Anyone help me get this?


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## spankone (Aug 31, 2011)

I'm running Panasonic 3100mah cells. I'll make sure they are full juiced up before I head out tonight. I've got a nice road ride planned. 

Have noticed that it flash between red and green. Which stops if you knock it down a mode. Then holds green again. 

The build really is good. The front is aluminium and the black fins. But the rear half is plastic. Which isn't a big deal tbh it's hard to tell its plastic. 


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## MirosPikos (Oct 3, 2011)

"But the rear half is plastic. Which isn't a big deal tbh it's hard to tell its plastic."

It is only plastic because of cover the heated body of light, I think so...


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## spankone (Aug 31, 2011)

Yeh I think your right. The plastic cover goes over the heat sink. 


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## spankone (Aug 31, 2011)

Ok geeks My Panasonic cells measured 4.20v this morning at 9am when I left for work. 8 hours later after being left plugged into the light head both cells measure 4.18volts. 

So both batteries dropped 0.02 volts over 8hrs. Is that acceptable levels of parasitic ? 


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## mattthemuppet (Jul 16, 2004)

unless you do the same test without them being plugged into the light, it's impossible to know if this is normal for your cells or due to the light. Then, if it is due to the light, you'd have to trickle charge them back up to 4.2V on a hobby charger to measure how much capacity has been used. My guess is very little - a drop from 4.2 to ~4.1V equates to about 250mAh capacity, so a 1/5th of that drop is likely to be pretty small.


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## spankone (Aug 31, 2011)

It's not normal for my cells I often leave them for a week and test them. 


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## betweenrides (Oct 19, 2010)

Ah, too bad. Not ready for prime time, eh? Fenix missed the night riding season for me anyway. Looks like a nice quality product but with some niggling design flaws. I am surprised by some of the documentation omissions. They should disclose type of battery to use (protected or not) and minimum mAh.


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## spankone (Aug 31, 2011)

After doing some more tests, battery drain is not noticeable. May be I was wrong and the drop was just due to my cells relaxing after being removed from the charger. 

Im glad I'm wrong  


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## pucked up (Mar 22, 2006)

*Update*

I have to correct myself on the Turbo Test I completed in the past. I don't know if Fenix has an issue with Turbo mode, I've search the web to see if anyone else posted review but didn't find any.

Anyways ran the test with 2 cells fully charge. Battery indicator went red within the first two mins. and then drop to High mode after 5 mins. Ran the test a second time with the same results.

To see if it was my batteries, I ran the test again using 3 cells. This time the battery indicator stayed green but drop to High mode after 5 mins also. If this was a heat issue, I had two fans on high blowing on it. The BT20 was barely warm to the touch. Ran this test a second time with the same results. I figure I would get more than 5 mins with 3 cells on Turbo but didn't.

If anyone else testing this light having this issue, it would be nice to know I'm not the only one.

I've emailed Fenix to see if anyone else experienced this issue. Waiting to hear back.


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## spankone (Aug 31, 2011)

In turbo I find the light goes red instantly. But doesn't drop out of turbo mode. Fenix have told me theirs an issue and have told their distributors to hold fire on delivering them. 

I'be found the fuel light in high goes from green to flashing red/green. The constant red. I've not drained the cells enough to see the next stage. 




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## pucked up (Mar 22, 2006)

spankone said:


> In turbo I find the light goes red instantly. But doesn't drop out of turbo mode.


Spankone, so you're able to maintain Turbo mode for longer than 5 mins?


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## spankone (Aug 31, 2011)

Yep. 


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## pucked up (Mar 22, 2006)

spankone said:


> Yep.
> 
> Sent from my iPhone using Tapatalk


Thanks, so must be my batteries not enough amps in them for this light on Turbo mode. Being that this is the only brand of batteries I have, my testing may have come to an end.


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## pucked up (Mar 22, 2006)

I like this video of cooling down the BT20 and water testing!


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## colleen c (May 28, 2011)

Vancbiker said:


> I have a hard time understanding how the battery voltage sensing would work right at all if you raise the input voltage to 12.6 using a 3S battery. The end of useful charge in that battery will be ~9V. That's higher than the starting voltage 8.4V of the original pack. I'm guessing the driver is programmed to change the indicator color or light output at set values. Maybe it senses the voltage when first turned on and that selects values based on the starting voltage. Anyone help me get this?


Keep in thoughts that there are buck driver that can be used in a wide range of input voltage from the battery. They basically buck the voltage down from a higher voltage and provide whatever current such as constant current or PWM to the LED. The XML led needs an average of 3.2v to be driven properly. So the driver will buck the voltage down to the proper volt at the LED. I'm not really sure where exactly does these driver sense the change. For all I know, they might be sensing the voltage after the regulation and not right at the battery input source. So you can have 3s power sorce or a 2s power source and it should not affect the driver sensor for the low voltage cutoff or indicator although one would be a nominal 7.4v and the 3s is 11.1v.

There might be an exception in this case for the Fenix light. The picture posted from pucked up show some circuitry in the battery pack holder. Not sure what it is. Low cutoff? Voltage regulator? Who knows.

Picture posted from member pucked up:


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## mattthemuppet (Jul 16, 2004)

that's not really how it works Colleen. Battery voltage is sensed as the difference between B+ and ground as LED voltage is determined by the current it's running at, which should stay constant as long as the battery voltage is above LED voltage + driver overhead.

So if you program a low voltage warning for a 2S pack (6.4V or thereabouts), that will be way past the point where a 3S pack is overdischarged (8.25V absolute minimum). The easier explanation is just that there's something funky going on with the driver, which is borne out by Fenix's temporary removal of the light from the market. I would have thought they would pick up basic stuff like this before releasing a product though, it's not like they're amateurs.

As for the board in the battery pack, it's not a PCB. For a start, there aren't enough parts and, second, 2S PCBs need a wire to go to the junction between the 2 cells (-ve pole of 1st cell and +ve pole of 2nd) to accurately sense the voltage of each cell. No idea what those 2 things do, but they don't have anything to do with preventing overdischarge that I can see.


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## colleen c (May 28, 2011)

mattthemuppet said:


> that's not really how it works Colleen. Battery voltage is sensed as the difference between B+ and ground as LED voltage is determined by the current it's running at, which should stay constant as long as the battery voltage is above LED voltage + driver overhead.
> 
> So if you program a low voltage warning for a 2S pack (6.4V or thereabouts), that will be way past the point where a 3S pack is overdischarged (8.25V absolute minimum). The easier explanation is just that there's something funky going on with the driver, which is borne out by Fenix's temporary removal of the light from the market. I would have thought they would pick up basic stuff like this before releasing a product though, it's not like they're amateurs.
> 
> As for the board in the battery pack, it's not a PCB. For a start, there aren't enough parts and, second, 2S PCBs need a wire to go to the junction between the 2 cells (-ve pole of 1st cell and +ve pole of 2nd) to accurately sense the voltage of each cell. No idea what those 2 things do, but they don't have anything to do with preventing overdischarge that I can see.


Thanks for clarifying. I'm still in that learning curve  So I guess that the Fenix driver must be programed to sense and know what the power source whither that 2s or 3s before knowing how to sense low voltage for the cutoff or mode change from Turbo to High. I do hope they get this problem fixed. I like the concept of multiple beam and hopefully others will persue the same course.


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## spankone (Aug 31, 2011)

They should have just kept it simple and made this a 2x18650 light. Seems pointless making it except 4x cr123s as well. 


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## pucked up (Mar 22, 2006)

colleen c said:


> Thanks for clarifying. I'm still in that learning curve  So I guess that the Fenix driver must be programed to sense and know what the power source whither that 2s or 3s before knowing how to sense low voltage for the cutoff or mode change from Turbo to High. I do hope they get this problem fixed. I like the concept of multiple beam and hopefully others will persue the same course.


The guys at Fenix have told me that the low voltage is set at 5.6v. The BT20 will step down when the batteries reach this point.

Too bad I can't measure what mah my batteries are at when charged/dis-charged. I would like to see if they're anywhere near the 2500mah it claims.


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## Vancbiker (May 25, 2005)

pucked up said:


> The guys at Fenix have told me that the low voltage is set at 5.6v. The BT20 will step down when the batteries reach this point.


This more like what I expected. So if one was to run this light on a 3S battery the voltage sensing would not work to protect the battery nor warn the user of impending shutdown.

If the battery had its own protection board then it would kick off the light. If the battery was unprotected the it would run down until the battery was damaged due to overdischarge.

For use with 2S 18650s, IMO the 5.6V should be where the light shuts itself off at. 6.2v for a low power step-down would be much kinder to the battery.


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## spankone (Aug 31, 2011)

My cells on Tuesday where at 4.19v before I set out and after my ride both cells measured 3.66v. I don't think I would like to run them any lower than that. 

Can some one remind me of the lowest voltage a cell can drop to before its damaged? 


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## spankone (Aug 31, 2011)

Part 2






It's a solid light but not quite there yet.

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## mattthemuppet (Jul 16, 2004)

spankone said:


> Can some one remind me of the lowest voltage a cell can drop to before its damaged?


most manus state 2.75V, although there's barely any capacity left after 3V


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## pucked up (Mar 22, 2006)

So I got some Panasonis 3100mah protected batteries from DX and tried a turbo run test. With my Trustfire batteries it would only last 5mins on turbo mode before drpping to high. The panasonic beat the 5 min mark, but then dropped to high at the 12 min mark. I was using the 2pk battery case that came with the BT20.

I would assume that there is an issue with the light or the unit as a whole doesn't like it when protected cells are being used. I stop the test after the 12 mins.


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## MirosPikos (Oct 3, 2011)

Officially there is a problem with driver. Manufacturer is actually solving this problem and then you can change your light. It can be resolved till the end of year.


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## spankone (Aug 31, 2011)

My bracket unscrewed its self from the light head the other day. Slightly annoying. 


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## spankone (Aug 31, 2011)

Well I've been playing with my light today. And using some camera to gopro converters I've been able to mount the light lower on the helmet. As well as gain the ability to quickly unclip the light to switch helmets.





































I recon I could also make a gopro bottle carrier mount. So I could clip the battery there. And use my kedge gopro bar mount to hold the light head. I should then be able to switch the light between bikes or helmets with in seconds.










Also fitted a clear lens to test it out.

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## pucked up (Mar 22, 2006)

Updated with video.


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