Bike Light Hacking
Converting a Bontrager Flare 1 bicycle tail light from disposable AAA batteries to rechargeable lithium power.
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components
Light: Bontrager Flare 1 tail light with 3x AAA battery compartment
Battery: 3.7v lithium cell salvaged from disposable vaporizer
Charging module: TP4056 lithium battery charging board with USB micro port, overcharge/discharge protection, and status LEDs
technical specifications
- Original voltage (3x AAA): \~2.9v
- Lithium cell voltage: \~3.1v
- Original housing IPX4 rating preserved
- Disposable vapes - repurposing the crappiest invention
- How to Reuse Disposable Vape Lithium Batteries
- r/AskElectronics
process
1. Disassemble light (lens, circuit board, battery compartment) 2. Test voltage compatibility with alligator clips 3. Solder TP4056 OUT +/- to light circuit board +/- terminals 4. Dremel battery compartment to fit lithium cell 5. Wire lithium cell to TP4056 BATT +/- 6. Reassemble housing with modified components
charging
Remove battery compartment, plug in USB cable. Blue LED indicates full charge.
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updates
2026 January
Over 2000 miles logged on this light so far with no issues.