The build started off, naturally, with a pair of Energizer D cells that hold 20,000mAh. A battery holder for these cells ... You can get D cell batteries everywhere, and what this build produces ...

Breakthroughs, discoveries, and DIY tips sent every weekday ... Mount the joule thief on a D-size-battery holder, and it makes a handy flashlight, one that gives your old batteries new life.

[Kounotori_DIY] uses ... for an 18650 battery holder and as you can see, it’s pretty slick. A little cylindrical container slides out of the assembly, allowing a spent cell to drop out.