I’m glad you borrowed a light before dropping the dough on a setup that isn’t stable. I’d highly recomend doing a little more testing before getting a “fatty.” Try mounting a can of soda (about the same size and weight) for a couple test rides. I’m guessing you will find the size and weight will make it very difficult to mount in a stable manner as it’s just too big and heavy for stability. I’ve had good luck with single 18650 lights in TwoFish mounts but they lack either the output or runtime you’re looking for. I’ve run a pair of lights on medium (a 501 and a C8) for a good mix of flood and thow - would that meet your needs? Is there any reason you don’t want a light with a cable and external battery pack?
M6 has a 1/4-20 threaded hole, same as camera/tripod mounts. Mount just needs to have a bracket a 1/4" bolt can go through and then a clamp for the bike tube. You can't mount a SRK like that (or a can of Coke).
This could possibly modified with the 1/4 screw and you would have the best of both worlds.
If you want to go back to the 26650 use then I have a shadow SL3 I might sell. PM for details. Would be a lot easier to mount than a fatty 4x 18650
Thanks folks,
Reason for not going for bike light plus battery pack is that I live in an urban inner city area and also use the bike for going to shops etc… Bike theft over here (Dublin, Ireland) is out of control. Every time I stop even for 5 minutes I would need to remove the light + battery pack. That’s too much hassle, an integrated light is the way to go.
I thought about an SL3 but its only a single 26650, my trip to work is 45-50 minutes each way but I need some reserve in case I forget to charge one day, therefore, at least 2 hours runtime. Not sure if an SL3 will do that.
If you mount them correctly fat lights should actually be more stable, its the Sumo effect ;), the centre of mass is more concentrated. There were a few posts on the MTB forums about SRK’s which actually come across as very good and cost effective alternatives to the $200+ specialist high lumen bike lights. Twofish make larger holders for things like water bottles and pumps which will probably work better than their standard flashlight mount. I design & build special purpose machines for a living so could fairly easily knock up a base block to match the radius of the torch. Also anything with a screw thread for a handle can be made work with a go-pro bike mount, also Lupine and exposure do handle bar mounts. Lupine actually do a lovely quick release handle bar bracket which could be adapted to suit, $$$ though.
I would consider one of these YL-U2
Only three cells but with the modes and variable output and 3400 pannys you should be able to get the use you want.
The light itself may be robust enough, but those lithium cells will take a beating. A cabled battery pack can be placed somewhere cushioned.
Just a idea for u to think about.
C8 light with reflector removed &. fenix mount. In your case u could carry a few spare 18560’s. Works like a chap. Nice and floody for her.
http://www.amazon.com/TrustFire-5-Mode-Flashlight-Generic-Packaging/dp/B005VCJNYG
http://www.bhphotovideo.com/bnh/controller/home?O=&sku=826981&Q=&is=REG&A=details
Btw. It has no wobble. The mount is strong. You can shop around for prices. I just threw the links to give u a idea.
I know of nothing that would run that long continuously with any 18650 or 26650 battery configuration, unless you added a custom battery pack with enough amp hours to do that. Certainly, not with any reserve left and then you are talking about hours of charging time, so you are really talking about a couple hundred dollars worth of battery packs and a hobby charger to begin with, along with a modified specialized light, for your application. In order to run four XM-L or XM-L2 U2 leds on “medium” (let’s say 1500 mAh each), that would mean your batteries would be drained at a rate of 6 amps per hour. You would most likely find times when you wanted to run on high, so then you would be closer to 10 amps per hour. I would recommend a battery pack that could do 10 amps per hour for at least 4 hours, for emergency conditions, or for as you say, when you forget to charge them. Now you are talking about 40,000mAh. That’s a lot of batteries! I mean to say, once you find out the real amp draw on most of these batteries, the continuous, daily, real life amp draw that they can successfully do, (if you want them to last for several months that is), then you will want to only hit them with about a 1/2C maximum discharge rate, so you are talking about a battery pack the size of a small car battery. If you take 3,000mAh batteries and figure a 1/2C maximum discharge rate, then you are talking about 1,500mAh didived into 40,000mAh, so roughly 26 of the 3,000mAh batteries in parallel, to give you the run time you require. Edit: If you did 1C discharge rate, that would still be 13 batteries in parallel.
It's probably better to look at some type of generator/alternator that you can hook up to one of your wheels, so that as you ride, you produce DC to recharge the batteries while using them. That way, you could use less of them and make it feasible.
EDIT: It's a worse case scenario and someone double check my math. I am so dyslexic I could easily have figured it wrong.
My TM26 will run for 8hrs (ish) at level 3, 540 lumens and over 2hrs at level 4, 1700 lumens on 3400 pannys.
Not worried about lumens. What is the amp draw per cell? That's all it's about really.
It’s urban cycling with street lighting as opposed to off road so ultimate lumens are probably not required. Can probably run on low or medium just fine. Cycle lanes over here are shared with busses and taxi cabs. Drivers of both seem to have a congenital issue with indicating and use of mirrors. Throw is required to warn vehicles that there is something behind them, flood is to spot potholes and raised drain covers. Hub generators aren’t really on for lightweight racers like mine, like putting a topbox & panniers on my Ducati.
Added: The Roche M170 and the Supfire are looking attractive….
or
Now, them’s r fatboys… 
Funnily enough, my kids call my brother “Uncle Buck”, thankfully all the cycling keeps that at bay here
Not sure what you mean.
My figures showed roughly, whether a set of cells would provide adequate illumination for the OP’s time frame, and give an idea of brightness v duration. May help in deciding which light to go for
Sorry not sure, just why draw per cell is that interesting. Whatever it is, at an output of 540 lumens there is a duration figure of 8 hours, which is more than the required 4 hours. A torch with a medium mode of that level and having a similar efficiency to the TM26, would mean there would be more than enough cell capacity for the OP’s requirements.
A $250 light in an environment where theft is rampant? Seems like a bad idea to me.