So let's look at the cost of everything. By my calculations the light, lens, battery case, 4x 18650 Panasonic cells, and a charger capable of charging 4 cells at once is going to approach or even exceed the cost of a good self-contained light that charges with only a simple USB cable. Plus there will be more light modes, and it's almost certainly much closer to its actual stated brightness than that Chinese junk.

https://www.amazon.com/Cygolite-Metr.../dp/B01IO12B30