You ve probably seen something like this.
I needed something that is bright, can be used on bicycle and also you can carry when you go exploring.
I made simmilar thing to DIY Perks portable sun but instead of using big CPU heatsink i used smaller one and whole body of flashlight to cool down LED.
Flashlight can work almost 1 hour on full brightness but i added potentiometer so i can dimm it and use it alot longer.
Battery that i used is 4S2P from old laptop batteries
Step 1: Building
I used 8 18650 batteries, 100W LED and 150W boost converter.
For monitoring batteries i got cheap Li-ion buzzer alarm that shows me voltage of all 4 batteries.
Fan is running on 6-7v and instead of step down converter i used resistor.
I installed small thumbwheel potentiometer from old headphones to control the light intensity.
I almost never use flashlight on full brightness becouse its really bright.
LED lenses could be added but since i use this in close enviroment i didnt put one.
Its really nice to carry this in forest becouse you can see everything in front of yourself.
Switch is on the handle so i can turn it on and off really easy.
Step 2: Battery
You can find cheap laptop batteries online or you can buy 18650s.
Good 18650 has about 2Ah capacity but they cost about 5€ per battery.
If you buy lot of laptop batteries you can get 2€ per battery and maybe even less.
When i tested batteries i used resistor across 18650 and i measured time.
First i soldered them together but later i got 8 holders and use that instead.
To charge them i made 4 cell balance charger from 4 usb charger and 4 TP4056 usb lithium charging boards.
Each battery charges with 0,5A of current so it takes about 4-5h to fully charge it.
Flashlight can be powered from any source from 10v to 30v that can deliver 100w.
I just need to unscrew 2 terminals that are going from battery to booster and connect any other source