I've used an iStick 50 Watt for 1 year out of at least 2 vaping. Started on a cig-a-like, moved on to a e-go, then a 20 watt iStick, and now I got myself a mod Wismec made specifically for Beyond Vape, called the Centurion. I was hesitant to buy any mod that has batteries that need to be charged outside the mod, as the 50 watts from the iStick worked pretty well, at .4-.5 ohms. But alas, I bought it, and it takes 1 26650 or 1 18560 in a sleeve. I bought a 2 bay charger, thinking I would need to eventually anyway, and that it would be unsafe to use the USB. So far, I find the whole replaceable battery thing really annoying. First off, I am afraid every time I put this thing on the charger that the battery is going to explode in my office or something, and second, the life of even the 26650 is not even CLOSE to the iStick 50 watt. Its a Brillipower 3500 mah 26650 battery that came with it (supposedly 60 amps, doesn't say what the current is but I think maybe 6.8 on the website). Now, my build that read .4 on the iStick reads .33 on the Centurion, so I have been using it between 65-75 watts. I wanted the ability to go up in wattage so I didn't have to pull for a long time on my Mod, the guy at my shops uses a 150 watt mod and vapes at 120 watts with the same build. But he must have to either carry 6 batteries around with him, or 2 18650s is a lot better than 1 26650. The whole point was to be able to push the batteries in the mod, but it just drains them. The battery lasts maybe a half day before I have to charge it again, which I do when its around 3.7 volts because I am scared of the thing. I do get a nice vape when its ok but I just find the whole external charging thing a pain. I almost want to return it and buy one of the Lipo pack 150 watt mods they have (for ridiculous prices), even if I have to use a USB more often, its much easier than bringing a stupid charger around with me everywhere I go. I guess the remedy would be more batteries? In which case I think I should just go for a dual 18650 and buy 2 sets of batteries.