I gave up on the small e-pens years ago, and moved to a mod. I'm an ex smoker, so...
I've got a sigelei 5-75 watt unit that I use for both, 510 thread, 18650 battery...
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Pictured is a concentrates atomizer, and my normal nic tank on the unit. IPhone build quality. The pens you'll replace, as the battery can't be changed.
Change the top, adjust the wattage and I'm off!
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Have been vaping now almost 6 years, making my own nic juice as well.. best choice I've ever made!