> I wasn’t sure how to find out what an “LI????77” was […]. I would be interested to learn non-LLM ways to figure this out though. There must be a way.

Reading https://en.wikipedia.org/wiki/Button_cell#Type_designation would have indicated a solution: The third character must be an R (for rechargeable), the “77” would be the height in tenths of millimeters (which makes for a good plausibility check), and then you can measure the cell’s diameter to obtain the remaining digits in the middle.

> I wasn’t sure how to find out what an “LI????77” was […]. I would be interested to learn non-LLM ways to figure this out though. There must be a way.

Back in my days I simply googled my way through the nomenclature of batteries. I feel pretty old, somehow.

Love this. I have a pile of nice Cygolites (both front and tail) that my whole family uses that are maybe 8 or 9 years old. Their capacities have largely dropped to the point that I need to charge them every ride or two. Maybe get about 90 minutes of use, down from 3-4 hours previously.

They're not user-serviceable by design but I've been pondering cracking them open and having a go at swapping the batteries. This post may inspire me.

I've got a pile of new 18650s lying around and hopefully the front lights use those!

I wouldn't worry about matching the exact model number of the battery. Instead, it's more important to get roughly the same chemistry and a capacity equal or maybe a touch greater (if technology improved in the last 10 years, capacity could be greater with modern parts).

Specific batteries go in and out of production. But as long as it's the same CHEMISTRY, voltage, and capacity, it's likely compatible. Chemistry tends to set the voltage, size sets the capacity.

Charge/discharge controllers and algorithms are based on these three bits of info.

In some cases, some chemistries are actually compatible with other chemistries. NiHM cells are largely backwards compatible with Ni-Cd chargers (but not vice versa). It's not good for the NiHM but they will actually take the charge.

In the Netherlands many people use these kinds of detachable bike lights. I've never came across soldered batteries in the dozen or so I've replaced batteries for. Not always cheaper, but just tossing the whole thing seems like such a waste.

Well done!

Thanks for sharing this. It's nice to see something not immediately turned into landfill junk. I ran into a similar issue awhile ago, and was able to replace the battery too. Not trivial, but very satisfying. Here's that journey: https://www.mooshwerks.com/2024/11/09/bike-light-hack/

On the subject of bike lights. Most of the current lights appear to use some LEDs which makes sense, of course. However the brightness of output light looks like completely unregulated.

On so many occasions I would get blinded by overly bright lights of an incoming cyclist during late evening ride.

Word of warning: batteries from AliExpress might not be the size it says on the tin.

Also: not all lights require soldering to change the battery. Some brands, like Fenix, offer lights where you can change the battery on the go.

I had a light from a lesser known Taiwanese brand - an INFINI Lava 500. At some point it stopped working, so I took it apart with my iFixit kit and inside was a 102660 battery (1700mAh instead of the advertised 2600mAh), so I bought a 102560 unit - 10mm thick, 25mm wide and 60mm long (supposedly).

It was a good few millimetres longer and didn't fit. What's worse - AliExpress stopped shipping batteries to my address, because due to safety regulations you can't ship batteries via airmail, it's just that one vendor who chanced it, so now I couldn't even buy a smaller replacement.

Local vendors didn't have anything nearly the same format, so I gave up and bought a LEZYNE LED Macro Drive 1300XL. Inside there are two 18650s wrapped in a pack that has a plug, so should they die, you can replace the battery without soldering.

I don’t know what it is with Julia’s writing but it always makes me happy. It reminded me of replacing the soldered battery in Super Metroid so I could save my progress again. As a cheapskate I used a regular battery and connected the wires mechanically.

This guy is funny, he spent~$20 and at least 10 hours to fix a product that can be purchased with $5.

I know it's slightly offtopic, but the brand I am using - ExposureLights - offers a battery diagnosis/replacement service for their bicycle lights.

Those are on the expensive side, but still, most brands would rather sell you a new one.

I recently had an even easier time changing the rechargeable battery in some mini Christmas lights. The unit was a solar panel in a box held by 4 screws. Took them out, and it was a regular AA nimh just slotted in there. Changed it out and the thing worked again.

I wonder how many people just chucked the unit when the battery wore out.

Love to see MEC gear - but I wish it were more repair friendly!

If it killed the first battery, won't it just do it again to the new one?

If anybody's interested in what the meta is for buying bicycle lights:

  1. Reflectors are the best for baseline visibility, they cost nothing and are reliable.

  2. The tail light is the important one.

    a) Try to find ones with a pulsating mode, blinding other road users by shining bright rapidly blinking lights into their eyes is not good, actually.

    b) If you've got the money, consider a radar instead.

  3. For the front, decide if you *need* illumination strong enough for you to see where you're going in darkness, or if you can get away with just being seen by others.

    a) For the former, make sure you get a front light that has a beam cutoff, preferably a lens-based solution. Then of course, install the light with a proper downwards angle, otherwise there's no point to the cutoff.

  4. Side visibility is important, this is usually accomplished by some see-through parts at the business end of the light.

  5. DO NOT use blinking modes at night. Blinking is for daytime, use only constant or at most, pulsating modes at night.

  6. BTW, the 2nd most important piece of equipment after your tail light is a mirror (>=2inch diameter).

Some recommendations:

• If biking casually or without a need for strong front light, honestly just get the cheapest lights you can get + some reflectors. Having any light at all gets you 99% there.

• Magicshine lights in general, I myself have the EVO 1300 for front and the SeeMee 300 for back. Proper lensed beam cutoff for the front, pulsing modes for the back, and good side visibility for both.

• Bontrager Flare RT for the back — small but powerful thanks to its focused beam. They also seem to have a front positional version but I haven't tried it.

Talk about burying the lead. This was a MEC bike light. It should have a replacable battery!

https://www.mec.ca/en/explore/sustainability-innovation

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The button-top vs flat-top distinction trips a lot of people up here: many bike lights ship with protected button-top 18650s, and a bare flat-top cell is a few mm shorter, so it can rattle or lose contact over bumps even though it's nominally the same battery. The other gotcha is cells with welded solder tabs vs spring contacts - if the original pack is tab-welded, a drop-in replacement sometimes needs a shim to make reliable contact. Worth checking both before ordering the replacement cell.

The wider point stands though: a bike light is a battery, an LED, and a switch, and the battery dying first is the most repairable failure mode there is.

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