As for the people hesitant to purchase anything other than a "quality" Joyetech product, I have purchased 2 650 twists in the last month. The first lasted 3 weeks before the button became displaced, and carefully opening it up to re-seat it turned into a disaster thanks to the "quality" soldering inside. That death of that one was mostly my fault, but recently ordered a red 650 and I don't think it's even been 2 weeks yet, but have been noticing the battery becoming loose where top fits in the battery casing already. Ate dinner at Chili's earlier, get home, reach in my pocket and this is what I pull out.
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Typically I attach the twist to my lanyard because it is my smallest battery, but have to pocket it now and then cause my kids think it's there to play with when I pick them up. So while a Vivi tank on an ego battery might not be super pocket friendly, it should at least be built well enough not to fall apart in your pocket from walking or sitting in the car. This has NOT happened to me with any other ego type battery and twice with the twists in a months time. Have to solder 2 wires back on, but the soldering is the easy part - fitting it back all together without another wire snapping loose is a different story.