Cordless tool battery, can it be used for a bike light?- Mtbr.com
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  1. #1
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    Cordless tool battery, can it be used for a bike light?

    Ok I looked up this question and its has been about 10 years since last asked. Since then a lot has changed, LED's and lithium batteries. So my question can it be done? Can we use a battery from a cordless tool like say a Dewalt 18V and run a bike light? Now I do realize that the average bike light is like 7-8V's so the 18V would fry the light. My thoughts though are for someone like me though. I have lots of these battery because I'm a contractor. If a cheap Chinese is use I could have a great safe bike light for under $20.00. These batteries are safe and the chargers are safe. I would be able to stretch the batteries usefulness beyond just using for work. Anyone want to take this project on?

  2. #2
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    You could probably do it with a voltage converter if you wanted to, but honestly it's pointless. The new batteries are so small and high capacity that anything else is just archaic.

  3. #3
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    I agree the batteries I have are the compact ones that are smaller and very light also the capacity is ridiculous when used with the shop light. I have some of those Chinese bomb batteries and I just thought this would be a good alternative.


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  4. #4
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    Yeah, those ultra cheap batteries are scary. My suggestion is to get a battery made with BAK cells, such as the magicshine or Xeccon batteries , or get one of the Panasonic batteries deals that ledoman has put together

    http://forums.mtbr.com/lights-night-...ce-995303.html

  5. #5
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    As said before if cheap chinese lights are to be used then stepdown converter is needed. Some are pretty cheap like 2-3$ on eBay as long as you stay below 2A.

    Otherwise you would need apropriate drivers (Taskled for ex.) which are very likely more costly than buying new battery pack mentioned it the thread linked above.

    BTW, what capacity are your cordless packs and how many cells (at least estimate) are in the pack? If the cells are of higher capacity (which I doubt) then can be used in building your own packs or replace the ones from cheapo Chinese packs. Cordless drills use mostly high amperage cells which tipicaly have less capacity, so it depends.....

  6. #6
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    Adding a stepdown DC-DC converter also decreases system efficiency. Finding additional uses for you existing batteries is a great idea, but sadly comes with many disadvantages. A few years ago it was fairly popular to use cordless tool batteries in the DIY light builds. They were best used in lights running 4-5 emitters in series.
    GoPro adapters for bike lights http://www.pacifier.com/~kevinb/index.html

  7. #7
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    I've been using Makita 18v batteries for years on my homebuilt lights. But keep in mind these are the correct voltage for the lights, and would not work with any 7.4v light

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  8. #8
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    I use Milwaukee tools and their shop light without a battery is $39 l may have to try a diy jober


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