Yeah, a fuse when you use anything other than a protected battery. ICR's actually come in the kits they sell; not the best, but doing.
The newer K100 and k101s actually ship with the new Kamry fuse. Mine did not. I use AW IMRs in mine. No problem.
Sometimes the telescopic portion is a bit wonky; some have reported that if tightened too tight, their K100 will keep firing. The top positive pin sometimes moves. It's not a true floating pin.If the telescopic is too too, or too lose there's some firing issues. I had some, and wasn't certain if it was the telescoping part, the firing button, the battery or the topper
device.
If you have a different battery, try that. Also try adjusting the telescoping or bottom cap. All devices seem to be a bit "fiddly" until you get to know their quirks.