There is a 3.6 volt NiMH rechargeable battery that comes in the light. SO, by free I refer to your out of pocket cost on batteries.
Step 1: Material
2. quick release light strap...most have a screw to change the mounting base, this is a Planet Bike
3. super glue
4. fingernail polish remover........or acetone
Step 2: Light base
Step 4: Break light down
Be cautious not to let any gears or gear shafts to fall out.