Okay, I am not an expert on Neopixels, and I'm sure one of the experts (jbkuma, Exar Kun, etc) will be with you momentarily to correct me if I'm wrong, but for pixel blades you need a High Discharge 18650 instead of the normal 18650s. pixel strips are power hungry. there's a lot of numbers floating around, and theoretical maximums of how much current a pixel blade can draw, but the base line comes down to this: most PCB protected 18650s will cut off if you draw too much current from them, and most pixel blades have power requirements above those limits. Hence, you need a High Discharge 18650. TCSS and most TCSS resellers sell them.
Also, while the strips have their own onboard resistors, it's generally considered good practice to solder in a resistor to the data line of the neopixel strip. I can't remember the exact resistance, bit it's something like any resistor between 300 and 500 ohms will do.