Julia Evans replaces 10-year-old bike light battery via makerspace soldering
Engineer documents successful DIY repair of decade-old rechargeable lights using an LLM to identify the battery model.
What to know
- Julia Evans successfully repaired 10-year-old bike lights by replacing a soldered battery, demonstrating that consumer electronics can be fixed rather than discarded.
- She used an LLM to identify the battery model when the marking was only partially visible ("LI???77" → LIR2477), raising questions about alternative identification methods.
- Commenters shared cautions about battery sourcing (counterfeit risks from AliExpress) and noted that exact model matching is less critical than matching chemistry and capacity.
- The post inspired several readers with similarly aged bike lights to consider attempting their own repairs rather than replacement.
The dispute Whether LLM use for battery identification represents pragmatic problem-solving or an unnecessary crutch when battery nomenclature standards and traditional search methods would suffice. · positions read across 25 posts and comments
Repair and reuse is satisfying and environmentally preferable to disposal and replacement.
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“Thanks for sharing this. It's nice to see something not immediately turned into landfill junk.”
mooshx · Hacker News ↗
Battery identification and sourcing require care; LLM identification should be verified, and parts from certain sources may not match specifications.
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“Word of warning: batteries from AliExpress might not be the size it says on the tin.”
Tade0 · Hacker News ↗
LLM-assisted problem-solving is pragmatic but traditional identification methods (nomenclature standards, Google) still work.
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“Back in my days I simply googled my way through the nomenclature of batteries. I feel pretty old, somehow.”
MrGilbert · Hacker News ↗
Julia Evans Engineer, bloggerLee and Lauria Makerspace peers
How it unfolded 2 developments, newest first · click a bar or a number to jump articlespostscomments
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Commenters offer battery identification alternatives and cautions
Hacker News users highlighted non-LLM methods for identifying batteries (button cell nomenclature standards, DigiKey search), cautioned about counterfeit batteries from AliExpress, and suggested matching chemistry and capacity matters more than exact model numbers.
“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.”
— dragontamer -
And please use **plastic** calipers to measure batteries!
2 more of the top 3 · 23 posts in this stretch
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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…
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The thing I love about jvns is she has this cheerfully fearless energy. Even when she writes about software stuff, half of it still has this wonderful tone of, "Hey, here's an aspect of computing that's new to me, let's discover/learn it together!" I wish I was that enthusiastic about pushing my comfort zone. The headline didn't grab my attention…
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Readers express interest in applying repair method to their own devices
Multiple commenters reported having older bike lights with degraded batteries and indicated the post inspired them to attempt similar repairs rather than replacing the devices entirely.
“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.”
— robot_jesus -
first by HN Best, 1d ago · also HN Frontpage
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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…
1 more of the top 2 · 2 posts in this stretch
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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!
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background
Evans reassembles lights and confirms successful repair — After receiving the replacement battery, Evans returned to the makerspace to desolder and replace it, then reglued the silicone casing. The lights now work for bike riding, though she is still waiting for a Mini USB cable to test the charging cycle.
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background
Evans uses LLM to identify partially obscured battery model number — Unable to fully read the battery markings ("LI???77"), Evans consulted an LLM which identified it as an LIR2477. She verified this matched her battery specs and ordered the replacement part, which arrived after about two weeks.
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background
Julia Evans successfully repairs decade-old bike lights with battery replacement — Evans located her 10-year-old rechargeable bike lights, found they only lasted 5 minutes after charging, and decided to replace the battery. She visited her local queer makerspace to use soldering equipment, cut open the silicone casing, removed the circuit board, and began the desoldering process after consulting iFixit guides and friends for advice.
What people are saying 18 voices from 2 sites · best of 25 · verbatim
- Yesterday
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Those battery numbers are (chemistry) in this case (LI) lithium, then the diameter in mm then the height in 10ths of mm (i'm sure there is a metric nominclature for that but I'm not sure what it is)
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Nice post but I suppose the true cost of this is never the monetary value that the repair took (the author talks about how monetary wise it was cheap to do) but the time (at least an hour longer than I would have wanted to spend) and while a fun skill to learn it’s probably not terribly repeatable without investing time in how to fix the next…
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Glad to read this. I have an overpriced umbrella with solar powered lights in it. It used to work great but now the lights only stay on for about 30 seconds now before turning of. I figured something may have gone bad with the solar panel on it - reading this makes me think that changing the battery out could be the fix instead.
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And this is why you don't ask an LLM such questions. An LLM will give you a random battery type as it doesn't have calipers nor hands to measure the size of the battery.
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How are the shipping rates from the US? There are a few of them on eBay.
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Desoldering can be a PITA sometimes. Particularly our HVAC heatpump blew a fuse and the mobo quote was $600 so I tried to desolder the leads but it was neigh impossible at any temps my desktop hako could output. Tried scratching off a surface film, using chemicals, nothing worked.I just ended up snipping the leads and soldering the new fuse inline…
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Where would you get those batteries other than aliexpress? The only [other place](https://www.newegg.ca/p/14R-09G6-005V6) I could find them was charging $43 per battery.
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Does anyone know of a back light that turns off after 5 minutes of no movement? I'm tired of backlight being out of juice just because I forgot to turn it off ...
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Congrats on the repair. Avoid batteries from aliexpress. I don't think they're dangerous but they may have a capacity lower than expected. Considering the complexity of the repair, you probably want batteries that last as long as possible (while being reasonably priced). Also, LIR2477, the 24 and 77 are the dimensions in mm so you don't need to…
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For removing soldered-in batteries like this - I do it on synthesizers a lot - instead of risking heating it up too much just cut the legs off and pick them out individually.Same for any multi-legged part with soldered-down mounting tabs like pots, chop 'em up and remove 'em a leg at a time. You'll put far less heat into the PCB, drastically…
- Sep 27
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I think it is neat that someone who is very expert in one area (software education) would try out doing something that’s not her area of expertise and publish the results.
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I did something similar recently. One thing you don't get to check before buying a light is the age of the battery within it. In two cases now expensive lights I have purchased had 8 year old LiPo puch cells in them, and died within a year of use.It was a surprisingly repairable light except for one catch: I could not find a pouch cell LiPo with…
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It's weird that rechargeable bike lights almost universally use soldered batteries. Conventional flashlights with onboard charging often use standardized cylindrical Li-ion cells that are field-replaceable by unscrewing the tailcap. They're usually 14500, 18350, 18650, or 21700 size, sometimes with a protection circuit stuck on the end (making it…
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This guy is funny, he spent~$20 and at least 10 hours to fix a product that can be purchased with $5.
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> 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…
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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.
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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:
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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.