Spark SX5 Shim, to allow use of 18650 cells in headband battery pack: $4.95
The SX5 headband battery tube will hold a 26650 cell, which is a 'fat' 18650 cell. You could shim your SX5 battery tube to hold 18650 cells with a custom cut piece of PVC pipe from Home Depot for a buck. That's what I had planned to do. However, as the pipe might rattle, would not leave any air space for cooling the battery, and would weigh twice as much, I decided to travel the world on a trip that would justify a reasonable tax write off, and look for the perfect shim. Finally I rented a bike near Gweilin, rode south, and stumbled across a foward looking 18650 shim factory that built a shim with O rings, so I bought 3 of these and after eating Bamboo Rat in a Hot Pot, came home to sell these shims and double my investment.