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Most (higher end) battery-powered bicycle lights have built-in Li-Ion battery or a battery pack nowadays. There seem to be no front lights using replaceable 18650 cells. Rear lights with replaceable batteries are widely available in my area (EU).

Li-Ion batteries have limited life and as such they limit lifetime of the whole light. If used everyday, the capacity is gone in one year. With replaceable batteries I can carry spare charged units for long night rides. 18650 batteries are widely available and seem to be natural "successors" of NiMh AA batteries for applications like bike lights, but such "evolution" didn't happen.

Is there any technical (not marketing) reason for this?

(I also use dynamo lights. This question is specifically about 18650 batteries.)

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Technical reasons: It’s harder and more expensive to design and manufacture a sturdy, lightweight, waterproof case which can be opened by the user. It’s also harder to design and manufacture spring loaded battery contacts which work reliably under heavy vibrations.

Most lights come with a built-in charging controller and can be conveniently charged via Micro USB or some other connector. Some 18650 batteries are only rated for certain voltages or currents which would make it harder to implement this fool-proof.

Personally I would be totally fine with having to open a few screws to access the battery. I’d also be fine with having to pick the right battery and not having a fool-proof connector style as long as the manufacturer tells me which batteries are compatible and the batteries are easily and cheaply available. But it seems there is just not enough demand and most consumers are fine with replacing whole devices every 4 years or so when the battery goes bad.

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  • I fully support all arguments in this answer. But for example head lights (I mean, which are put on the head) with replaceable 18650 battery are quite common, while all these arguments equally apply. What makes bike lights different?
    – Konstantin Shemyak
    Aug 25, 2021 at 13:06
  • Perhaps there is a gap where 18650 is vastly overpowered for regular cycling lights with intensity levels legal on-street in Europe, but inadequate for incredibly powerful offroad lights? Only someone who actually works at a bike light manufacturer could really provide the authoritative answer on why they feel there isn't enough market for such a product.
    – Affe
    Aug 27, 2021 at 22:44
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As Criggie notes, there are plenty of flashlights using such batteries, and I find some make excellent headlights. I've mounted such lights to my handlebar and/or to my helmet.

The characteristics I find useful are:

  1. Good quality machining of the aluminum shell, and O-rings to prevent water ingress.

  2. Multiple brightness modes, including both high-lumen flood (perhaps 200 lumens) and medium/low lumen blinking. High-lumen mode should last at least 1-2 hours on a single 18650 charge.

  3. Wide flood with uniform illumination over the field rather than a strong center bright spot and weak illumination to sides. A wide zoom range with quality glass lens can work well for this.

  4. Sufficient builtin heat dissipation that LED can run at high lumens for more than an hour without either LED or battery having overheating issues.

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    There are countless such headlights. Replacable is the rule there, not the exception (in the higher quality and brightness sector). But the question is, why there are no such bike lights? Or are there any?
    – Vladimir F Героям слава
    Aug 25, 2021 at 5:42
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    @VladimirF I have found it difficult to get such a flashlight with char. (3) above - a wide, uniform illumination field, and sometimes the other char. as well. In any case, what do you mean by a "bike light"? I consider my flashlights (and their mounts) "bike lights" and dedicate them for that purpose.
    – Armand
    Aug 25, 2021 at 7:25
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    After juhist arrrives, he will explain to you that a proper bike light must follow the German norm that prescribes the way the light cone is illuminated to avoid blinding other traffic. Even if you leave that issue aside, a proper bike light - for me - comes with a possibility to be mounted directly on a bicycle without resorting to various bodges or inventing custom 3d printed mounts.
    – Vladimir F Героям слава
    Aug 25, 2021 at 7:47
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    You are likely correct about the first part, on the second I consider my $10 ebay/amazon handlebar light mounts neither bodgy nor 3d-printed. Perhaps I should instead obtain titanium ones for proper bike community approval :)
    – Armand
    Aug 25, 2021 at 7:54
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    I’m not juhist but I have to agree with Vladimir. Not blinding other traffic is important and for that you need a proper horizontal cut-off. A circular light cone (as it’s typically found on handheld flashlights) is completely unsuitable for road use, unless it’s very low power and only there to make you more visible.
    – Michael
    Aug 26, 2021 at 9:25
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I use this head mounted light that uses 18650 batteries.

It doesn't need to be mounted on bike, thus can not be stolen.

enter image description here

From https://www.ebay.com/itm/254653073362

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    That’s only suitable for off-road use because it blinds other road users.
    – Michael
    Aug 26, 2021 at 9:26
  • Not if it has adjustable light levels which most do. @Michael
    – fixit7
    Aug 26, 2021 at 14:33
  • Are you affiliated with the seller? It makes no sense to post some particular type of headlight. It also does not answer the actual answer asked.
    – Vladimir F Героям слава
    Aug 26, 2021 at 16:35
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    It's a good point, but is also not a bike-specific light, and has the potential to be misused on the road. However these kinds of rigs would be more found in off-road usage, where the enormous illumination/spill is definitely useful.
    – Criggie ♦
    Aug 30, 2021 at 0:10
  • @Michael off road riding is still riding. We accept both kinds, so I'm going to leave this as an answer. It would be a poor choice to ride with this kind of light on the road.
    – Criggie ♦
    Aug 30, 2021 at 0:12

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