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My family uses lots of bicycle lights and I need to buy some more now because they break or get lost or stolen.

I'm trying to work out whether it is better to buy the bike lights that use AA or AAA rechargeable batteries, or a bike light that has a built-in battery which needs charging via a USB cable.

I have a good battery recharger which will not only charge batteries using different modes, but will also "recondition" the batteries. This function refreshes the capacity of the battery to either take more load, or to hold it for longer (or both, I'm not sure).

I'm not sure how effective this is but I always sense that some batteries run out a lot quicker than other ones and then I put them through the recondition programme.

It strikes me that it's impossible to recondition a built-in battery because my battery charger doesn't have a USB port.

Is this something I should take into consideration when choosing my next bicycle light?

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    The battery charger that "reconditions" sounds like marketing bullpuckey. The only thing that would be remotely useful in that space would be doing a deep discharge every 20-30 uses on a nickel-cadmium pack to avoid memory effect. But that's a peculiarity of that one obsolete chemistry, and enen so, you can do that yourself for free by leaving the light on LOL.
    – Harper - Reinstate Monica
    Commented Mar 28, 2023 at 20:09
  • Just discovered that likely only 15% of Li is recovered during Li-ion battery recycling nature.com/articles/d41586-023-00915-3
    – Adam
    Commented Mar 31, 2023 at 16:50
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    Wow, that's it. Some lab level experiements by a small team is the culmination of the recycling effort. That's almost as bad as the fact that most of our power comes from burning coal. Seriously, "progress" is a thing :) The Wright Brothers didn't start out with the 747.
    – Harper - Reinstate Monica
    Commented Mar 31, 2023 at 18:57

4 Answers 4

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My heavy recommendation would be hub dynamo powered modern LED lights (with a supercapacitor for providing light after stopping).

However, if for some reason this is not an option for you, the second best choice is AA powered light and Sanyo/Panasonic Eneloop batteries. Make sure to purchase a good charger (like Maha MH-C9000 Pro) for them because poor chargers fry your batteries in no time.

I have several 15 year old Eneloop batteries that are still working fine. They have over 90% of capacity left.

Eneloops have very slow self discharge and long lifetime.

AAA batteries cost about as much as AA, but have fraction of the energy so to provide adequate lifetime you need so many AAA batteries you can't fit them to one charger at a time. Thus, I recommend AA.

USB charged devices almost exclusively use cheap chinese Li-Ion cells. My experience has been that in mobile phones, they start swelling in about 3 years. If the batteries in a USB charged device fail, replacing them could be tricky. However, with AA batteries all you need to do is to buy a new battery.

A single Eneloop has 2.4 watt-hours of energy. With a decent light, it lasts approximately one hour or maybe little less. With four Eneloops, you can get little over 3 hours of runtime. With a dynamo you would get infinite runtime.

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    Interesting praise for Eneloop. The consumer test which.co.uk/reviews/rechargeable-batteries found Eneloop Pro AA are the best, but Eneloop AA (not Pro) are significantly less good and several other brands are better. Thanks for the pointers.
    – Adam
    Commented Mar 12, 2023 at 15:18
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    I disagree that pro should be chosen. Pro has more capacity, but faster self-discharge and less durability. My opinion is that it was a major mistake by Sanyo/Panasonic to enter the high-capacity competition with the Pro model. The basic model is the one that should be chosen. I suspect 15-year old Pro batteries wouldn't have more than 90% of their capacity left.
    – juhist
    Commented Mar 12, 2023 at 15:31
  • Don't forget the rather large upfront cost of dynamo lights. I like mine, but even a budget setup cost more than many bikes.
    – Chris H
    Commented Mar 14, 2023 at 16:39
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Frame challenge rather than an answer.

You're asking about bike lights with different types of batteries from a sustainability perspective.

The most sustainable type of bike light is powered by a dynamo.

  • The most ecological/sustainable type of battery is no battery at all.
  • The energy source would be (mostly) human muscle power (assuming the bicycle is human powered and not electric), which I would expect to be more ecological than any other alternative, but I don't have evidence to back this up (it might depend on your diet).

As a bonus, they're also harder and less attractive to steal, because they're permanently fixed to your bike and are useless on bicycles that don't have a dynamo. Most dynamos are built into the wheel, so thieves would have to steal the entire wheel, which is hopefully secured with a good lock.

Finally, there even exist bicycle dynamos with which you can charge devices by USB, so you can charge your mobile phone on your bike :) (NB: not cheap and not terribly useful unless you're going on a bike tour away from civilisation for multiple days).

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    Also the best dynamo is a hub dynamo. The ones that continue providing light after stopping are usually implemented with a supercapacitor rather than a battery. Supercapacitors have longer lifetimes than batteries.
    – juhist
    Commented Mar 12, 2023 at 9:07
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    @Adam I think they're more common in the front (the rear wheel might have internal hub gears) but it's true that installing one means a new wheel or rebuilding an existing wheel.
    – gerrit
    Commented Mar 13, 2023 at 7:46
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    The energy source would be (mostly) human muscle power (assuming the bicycle is human powered and not electric), which is also more ecological than any other alternative. I doubt many people here are fuelling their rides on steak, but the carbon footprint of that is going to be far worse than a typical electricity generation mix. I looked into something similar here.
    – Chris H
    Commented Mar 14, 2023 at 16:38
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    @gerrit for a worst case diet and a best case electricity generation mix, the emissions per unit distance are almost certainly better on the e-bike. But the extra manufacturing emissions would require a lot of distance to offset, and batteries in particular cause non-carbon pollution in manufacturing. On the other hand a largely plant-based diet and typical generation involving some fossil fuels looks pretty clearly in favour of human power.
    – Chris H
    Commented Mar 15, 2023 at 8:01
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    ... Going further, cycling is good for health (though e-biking can be almost as good if it gets you out more) . Healthy people live longer, increasing their lifetime emissions, but need less healthcare and healthcare can be quite polluting
    – Chris H
    Commented Mar 15, 2023 at 8:02
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USB-rechargeable things are essentially always lithium ion. Lithium ion batteries can't be meaningfully reconditioned, and anyway the charger is inside the device (your phone "charger" is just a power supply).

When I'm not running dynamo lights, or when I need additional lights (including for night mountain biking which needs far more illumination than road riding) I tend to use USB-rechargeable lights. I have been known to replace the batteries in them, and recycle the old ones, rather than replacing the whole light.

Something else I've done with 2 front and one rear lights, with failed batteries and/or electronics, is convert them to run off a USB battery pack - which I would have and carry anyway. Typically for a front light this means fitting a new controller board that can accept 5V. That's what I plan on using for an all-nighter next month, as I don't have time to build a dynamo wheel for that bike, and I'm not sure I want to.

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  • Handy if you have those skills. I could use a soldering iron, no problem - it's just knowing what electronics to buy (and where) that's the important bit.
    – Adam
    Commented Mar 15, 2023 at 17:17
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Not all batteries are the same.

NI-MH for example don't like to be recharged before fully flat, but doing a full discharge cycle, will mostly fix it. 3 cycles will do even more. Ni-cad also don't like to be recharged before fully flat, and the damage is not fixable. The above phenomenon is often called memory effect.

Lithium batteries don't have this problem.

Multi-cell batteries, may need balancing. This will be built into its integrated charger.

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  • This is totally and completely false. NiMH can be recharged before fully flat. The reason in some cases you should have flat batteries is poor chargers: a timed charger should ideally be used only for flat batteries. But with proper negative delta-V termination, you can charge a battery in every single case. So-called memory effect only occurs in satellites: if the battery is discharged to exactly the same state-of-charge (like what occurs for satellites orbiting Earth), it will remember that state-of-charge. In terrestrial applications there is no memory effect, but there are poor chargers.
    – juhist
    Commented Mar 20, 2023 at 18:10
  • I have seen this effect here on earth. Not a very big effect in recent years. Mainly on older stuff. But, even a new toothbrush seem to suffer a little. Every so it seems that the battery is broken, I let it run all the way down and recharge, and it mostly fixes it.
    – ctrl-alt-delor
    Commented Mar 24, 2023 at 21:28

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