It's made so one can replace the battery, but has a USB port (expected to be above average quality) and it made in a way to encourage use of the USB port. Whatever 18650 batteries ProVape is selling will work well with the Radius, flat top or button top. And, it can be used like a pass through.
If I recall correctly, I believe that 0 in 18650, 18350 etc. is for Round.18 -- radius of battery, 65 length, 0 for shape, in mm.
Do those kind of batteries come in anything but round? (Not being snarky)