Re: 18650 battery pack assistance needed.
This might be something you already know, but with homemade battery packs and running, you'll have to be very careful with strain relief and good cords. Do not underestimate the fatigue failure potential of cords when running and when the cord is basically unsupported between the lighthead and battery pack. I had a long learning experience when I was running a homemade external battery setup on my Princeton Tec Eos more than a decade ago, where I'd have the cord break every several days, and then I'd make improvements with different cables, shrink wraps, and strain relief setups, and then keep reiterating and fixing stuff. Then cords that kept breaking on the then new Magicshine 808 P7 lights half a dozen years (?) ago (though the bikers that used the light didn't have the same complaints). Now I just use an off the shelf setup and prefer to keep the battery pack on my Yinding/Gemini on the back of the headstrap so there isn't cable flapping around.
The bounce with every footstep when running, especially when the battery pack is on your body, puts way more flex cycles into the cords than use on a bike for example. Not sure how your waist belt setup will look like, but be careful of unsupported cord. Make sure the strain relief isn't too stiff so the cord breaks at the edge of the strain relief. Not that you'll have this problem, but something as little as the extra stiffness of the solder on a repaired cord that is bouncing around from running, even with good heat shrink on it, will produce a stress riser that will cause an eventual failure, at least for the typical 22 AWG cords used in lights like Magicshine/Gemini/Gloworm. Why not just get an off-the-shelf battery pack? You can get 6 and 8 cell packs from Magicshine or Gemini. I'd personally just get two off the shelf 4 cell batteries if you need that capacity, so if one fails, you still have another. Switching between batteries can easily be done on the run.
This might be something you already know, but with homemade battery packs and running, you'll have to be very careful with strain relief and good cords. Do not underestimate the fatigue failure potential of cords when running and when the cord is basically unsupported between the lighthead and battery pack. I had a long learning experience when I was running a homemade external battery setup on my Princeton Tec Eos more than a decade ago, where I'd have the cord break every several days, and then I'd make improvements with different cables, shrink wraps, and strain relief setups, and then keep reiterating and fixing stuff. Then cords that kept breaking on the then new Magicshine 808 P7 lights half a dozen years (?) ago (though the bikers that used the light didn't have the same complaints). Now I just use an off the shelf setup and prefer to keep the battery pack on my Yinding/Gemini on the back of the headstrap so there isn't cable flapping around.
The bounce with every footstep when running, especially when the battery pack is on your body, puts way more flex cycles into the cords than use on a bike for example. Not sure how your waist belt setup will look like, but be careful of unsupported cord. Make sure the strain relief isn't too stiff so the cord breaks at the edge of the strain relief. Not that you'll have this problem, but something as little as the extra stiffness of the solder on a repaired cord that is bouncing around from running, even with good heat shrink on it, will produce a stress riser that will cause an eventual failure, at least for the typical 22 AWG cords used in lights like Magicshine/Gemini/Gloworm. Why not just get an off-the-shelf battery pack? You can get 6 and 8 cell packs from Magicshine or Gemini. I'd personally just get two off the shelf 4 cell batteries if you need that capacity, so if one fails, you still have another. Switching between batteries can easily be done on the run.
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