Does anyone make a tail light that lasts a super long time? Like 18650 battery?
I bike daily and drive 1x a month. Honestly, I’m tempted to just do a Dynamo Generator Hub front and back. I have a lumintop rear light and don’t want the hassle of regular charges.
I’m not aware of a tail light using a 18650,
This Magic Shine has an 1600mAh battery which is close to a low capacity 18650.
I bought six of these Xanes light (when the price was lower) and carry on my ride and switch them when the needed. I only carry two at at time I get about 1 1/2 - 2 hours runtime from each one.
Do you need blinky modes? Any other requirements? Budget?
For back of the envelope calculations:
You run a light for eg. 1hour for each weekday (264/year).
You use a 3100mah capacity cell.
You can use ~11.5ma per hour to get the cell to last a full year, which isn’t a lot.
There are manufacturers that use a proprietary 18650 battery inside bike lights but none that I know of who offer tail lights with extraordinary run times at an intensity worth using. No light would run more than several days, much less a year. Even using a quality Panasonic 3,400 mAh 18650 battery is not going to be more than several times the capacity of the 650 mAh lithium polymer battery in the inexpensive Lezyne 3-LED clone (100 lumens) that I use for daytime running lights. I have experimented with modifying a pair of these lights to run on a single 18650 battery. The unmodified light will run for at least 6 hours between charges which for me is charging it about every 4th or 5th day. I have yet to try it on the Panasonic battery but one of the cheap Chinese batteries that is several years old will double that time. I expect the Panasonic battery will run about 30 hours. Here is the light that I am using: 2×USB Rechargeable LED Bike Lights Set Headlight Taillight Caution Bicycle Light 741802829610 | eBay I mount the light and battery case on a short plastic tube and use a “360 degree flashlight holder” to hold both an a bike. New 360° Swivel Bicycle Bike Mount Holder Clip Clamp for Led Flashlight Torch | eBay It’s a lot easier to mount the light on a tube that will fit the flashlight holder, use the flashlight mount, and just pull the tube off and take it inside to charge with the USB cord that comes with the lights. It stays on securely but takes only seconds to install or remove. The same flashlight holder works with flashlights using the 18650 battery so you can use the same holder for a night riding light.
Some kind of blink would be nice.
Budget is < a dynomo wheel hub, wheel and dynamo friendly light… which is what $400 or more?
$100 is very reasonable for this project.
I was being a bit hyperbolic, I’d be happy with once a month or two. That said, the year long goal is pretty easy to accomplish.
A decent tail light (lumintop) draws 22.5 mah an hour in blinky mode. A 21700 battery can provide 5,000 mah which is 227 1/3 hours of night riding. Or, 37.4 minutes of night riding each day with no breaks. That’s more than enough to last me a year.
Most lithium-ion batteries have a self-discharge rate of between 0.5-3% per month. So even accounting for self-discharge, I think this is doable with a 21700.
It boils down to size, weight, power, and cost.
What you are looking for may exist but may be too expensive, or too big, or not powerful enough.
I would list the pros and cons of the top five or ten lights that meet your criteria.
Sometimes the answer is right in front of you. You will have to train your mind to select it.
It would be a tiny little blinker. The kind that would be powered by a little solar panel not a dynamo
I want a $9 lumintop BT1 tail light + a 21700.
That’s $20 in parts.
I might just make one myself.
This is overkill, but I think I can build what I want for less than $25 of components.
Well, yeh, if you take out the current battery and make a waterproof external 21700 holder, that should be perfectly doable.
I suspect charging/battery management board is on the main PCB, but might be integrated into the lipo pouch.
Edit to add- the tricky part might be a waterproof 21700 solution. I’m on search for something similar for a similar remote battery, probably 3D printed with copper contacts then waterproofed with silicone sealant. I don’t “do” 3D printing though 
Build your own is the way to go. Mine is an S2 with a red LED, floody TIR lens. Modified Biscotti firmware on a 4x7135 driver: steady, blinky (which I never use), voltage read out. I charge it a couple times a year haha.
For whatever it’s worth, I’ve done this a couple of ways and have been using it for several years now.
The silliest way is the most recent, where I have an Emisar DT8 and a Fenix ALD-10 + ALB-10 tucked under my saddle with a GoPro rail adapter. It throws a lot of light but it’s not as waterproof as I would like it to be. I don’t actually use this, though I do still have the quick release installed and I do carry the DT8 in my bike bag. (I kind of want to replace it with a DT8K though…)
Only very slightly less silly is a pair of Emisar DW4’s mounted on quick release rails on my backpack, which throws a tremendous amount of light - actually too much to be useful. Definitely go with the buck driver upgrade if you’re going to try this.
The least impressive but most useful setup I have is a pair of Orfos Flare Pro side lights and a Hope District+ rear light running from a 4×18650 battery pack. I have been running this setup since 2019. I have to charge the battery pack about 4-5 times a year. Alas, Orfos went out of business last year; I’m currently experimenting with 12V motorcycle LED strips and a voltage booster as a potential replacement for when my current side lights give up the ghost.
If you want to go super simple, an Armytek C2 WR and a Klickfix quad minibloc plug & socket would probably do the trick.
Well, it depends on how many 18650s would fit in the light. Add one or two dozens and perhaps you could have a useful light that you could charge only 1x an year… 