Only requirement is that it be a 18650 battery.
A mini with an 18650 battery?
IPV Mini or Sigeleli Mini. The istick doesn't use an 18650.
Actually, the iStick does use a 18650 battery. The iStick 20 and 30 has one in it, the iStick 50 has two in it.
i use a mechanical mod now, will 30 w be enough power or should I get a bigger one?
The Sigelei Mini does have a USB charge port. it is on the bottom of the mod.As what happens with hard disks, buy the biggest you can afford. Even if you don't use it, you know it's there.
As for replaceable batteries, do yourself a favor. The Sigelei doesn't have an USB port. Get yourself an IPV mini2. You'll have a lot of PV for 20 bucks more? Not worth it. Sigelei has never worked for me.
What do you mean by swivel battery cover? The Sigelei Mini has a magnetic battery cover that opens on the side. It just lifts off, nothing swivels.Definitely not a Cloupor. The Sigelei is nice, though it does have a swivel battery cover which might get chipped up after a while. The IPV mini 2 gets recommended a lot here but I don't know about it. One battery pushing 70 watts sounds iffy.
Actually, the iStick does use a 18650 battery. The iStick 20 and 30 has one in it, the iStick 50 has two in it.