Ten-year-old bike lights revived with a battery replacement

Rechargeable bike lights bought ten years earlier charged fully but then ran for only about five minutes before switching off. That was the starting point for a repair write-up published on September 27, 2026 by Julia Evans, who decided to replace the battery rather than buy a new set of lights.

Evans has long wondered whether old electronics can be fixed, and a dead battery in a light she still owned looked like a good first project.

Cutting into a sealed light

The lamp felt like silicone, so the first step was to cut the outer shell along a line that vaguely resembled a seam. Some silicone tore, but the circuit board came into view. A few screws held it in place, and she removed as few as possible for fear of losing them or not getting them back.

Desoldering the old battery was new work. Following an iFixit guide plus advice from two friends, she used a desoldering pump to take off most of the solder, then separated the parts and paused regularly so the battery would not get too hot. A metal tab on top of the cell looked like an obstacle, until it turned out the replacement battery ships with that part attached.

Reading the cell markings

The old battery carried a partial marking that read something like "3" and "LI???77". Unable to identify it, she asked a language model, which answered "LIR2477"; looking that up, the part matched her cell exactly. She notes she would prefer a route that does not rely on a model, and that a friend showed her how to search on DigiKey, which did not stock the part.

Two batteries and silicone glue came from AliExpress: roughly $3 per cell and $8 for the glue. The parts took about two weeks to arrive. She then soldered the new batteries in, refitted the remaining screws after dropping some of the tiny ones, glued the housing and let it cure for 24 hours. The old cells went to a collection point that accepts used batteries.

Repair instead of replacement

The lights work, and she has already used them on night rides. Whether the repair lasts is still open: she has not yet needed to recharge them, and had to order a Mini USB cable since she no longer owned one.

Evans says plainly that she has little electronics experience and that her post contains no safety advice. She did the soldering at a community workshop where she is a member, and recommends such spaces because help is at hand. Parts for the whole job came to about $20 CAD.