After trying unsuccessfully several commercial bike flashlights, I decided to make me one that cover my needs:

- Lightweight and very small size.
- Rechargeable to prevent the continued waste of AA batteries.
- Cheap!!!
- Powerful and long-term for long night cycling routes.

Due to my limited knowledge of electronics, I assume that the circuit can be improved, so any help comment  or suggestion with this, will be welcome ;)

Step 1: Materials Needed

- Old Cellular phone with working battery and charger (as charging station).
 - Rf switch cable TV adapter from an old video game console or some similar size plastic case.
- Hard disk or some electronic device with contact pins.
- A small switch
- 10 white ultra bright leds with prototyping board for welding circuits.
- Solder
- Bicycle clamp from a broken bike light
- Wire

How about a Mentos box?
Nice idea to use a telephone battery but its quiet dangerous. Because you use it on a bike, it could get wet and short circuit so you have to make sure no water gets inside. And without some current limithing its not very safe in use. But al together its a good thought because of the high capacity of the battery you have a long lasting light.
I've been reading about the dangers of using this type of batteries, but due to my limited knowledge of electronics I have not been able to improve the prototype. I hope, at least, this design can serve as inspiration to other users with knowledge of electronics to make a better and more secure device. Thank you all for your comments.
If you put a glase fuse of 250mA in series with the feeding wire of LEDs you could at least prevent a shortcircuit to cause damage to the battery. 10 led x 20mA = 200mA nearest fuse above is 250mA
Great idea! I had a similar instructable planned. Guess I'll have to come up with something different now.
That battery appears to be a lithium-ion or lithium-polymer battery, since that is what most phones use and have used for some time now. even though they are labelled 3.7v or 3.6v the full charge voltage is 4.2v. This is a bit too high for the leds and will probably cause them to burn out eventually. Also this type of battery should never be discharged below 3v or they will quickly lose the ability to be recharged.
You need some kind of current limiting resistor or those LEDs are going to start burning out, i dont know how many volts your battery puts out so i cant recommend a resistor size. Other than that it is a pretty clean design
Thanks for the help!!! Battery outs 3,7 Volts.

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