Just for what it's worth, I tracked down the battery that is on the HCigar website from their pic, it's a Movfo 26650 3.7 V 4200 MAH 40A Battery
INR 26650 and on FastTech website it says it's 65mm length. So I'm guessing if any battery is even a little over that, and the ijoy's are 65.74mm, and assuming that the measurements are accurate, the ijoy's I got off of ebay listing, it would be interesting to know if anyone who's still using a 26650 with NO problems could tell us the brand and length of the battery. I agree we shouldn't have to go thru this at all but there are so many size differences in the 26650's and even the 18650's that HCigar should be telling us what those specs are, other than that you all could be right that they should've tested for this, but short of making the space where the battery goes so that it only fits a correct one or they did a lousy job putting it together, we have to be careful. I'm wondering about the ones in my headlamp, not same kind, that rest behind my head lol, people are out there putting these in all sorts of things just to get more power out of their flashlights etc. But for my headlamp I just ordered button top18650's thinking it's just a different type of battery but is standard sized like we all grew up with. I'm just sticking with using the 18650's for my HCigar VT75 Color.