Okay, so my brother's girlfriend ordered her ecig kit from Knight Sticks. From what I've read so far, they seem to not have the best business practices and she kind of got caught up in it. She was using the product without any real complaints until she lost her battery. She called customer service (and I use that term lightly) to order another battery when she was told that she would have to purchase a whole new kit ($99!). The lady was quite rude from what she said and decided to talk to me about my 510. I told her that I don't really use my stock batteries anymore and that I would set her up with mine so she didn't have to buy smokes (bleh), and to give me one of the cartomizers from her kit. I did some research without any real finds, but decided to see if the carto would fit on my stock 510 battery. It did! Not only does it fit, and fire, but it works really well! Better than my stock 510 atty at 3.7v. Maybe a lower resistance? Don't know... maybe the gurus here could shed some light, but I wouldn't mind trying a few more of these. One more thing... while it does fire on my stock 510 battery, it will not work on any of my mods. Don't really know what that's about. So anyway, for anyone who lost their Knight Sticks battery, buy a stock 510 battery, plug it in and vape away!!