Converting a Bontrager Flare 1 bicycle tail light from disposable AAA batteries to rechargeable lithium power.

components

Light: Bontrager Flare 1 tail light with 3x AAA battery compartment

Bontrager Flare 1 circuit board

Battery: 3.7v lithium cell salvaged from disposable vaporizer

Lithium battery extracted from disposable vaporizer

Charging module: TP4056 lithium battery charging board with USB micro port, overcharge/discharge protection, and status LEDs

TP4056 charging module

technical specifications

  • Original voltage (3x AAA): ~2.9v
  • Lithium cell voltage: ~3.1v
  • Original housing IPX4 rating preserved

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

Test fit with alligator clips

charging

Remove battery compartment, plug in USB cable. Blue LED indicates full charge.

Light charging via USB

updates

2026 January

Over 2000 miles logged on this light so far with no issues.

resources