specifically, Can i use a Blu cartridge with a NexGen battery? actually, i already have the NexGen starter kit and bought some Blu cartridges because i really like Blu's the best, but the NexGen kit is much cheaper. and i notice that no air is getting in. it just feels like i'm sucking on a pencil. but when i exhale, plenty of vapor comes out. can someone please tell me a way to make this work the way it should? like maybe screwing the cartridge on differently or something? Thanks.