I have a Smoktech mechanical (fully) mod that is called the telescope.
There are NO wires, no circuit boards...no electrical anything other
than the power supplied by the battery that you insert into it. It is
activated by pushing a button which will complete the connection to
the battery (the other part is at the top of the mod). With this type
mod, you can use an array of batteries ....right now I"m using a 18350
but usually use a 18650. There are several other sizes that will fit
because the tube of the mod "telescopes" into itself to accommodate
several sizes and types (flat top, button top, li-ion, li-po, li-mn)
They are all metal...and can be a bit heavy....but they don't have
easily breakable parts. The ST Telescope has a wheel that can be
screwed down to prevent accidental firing. The big advantage is that there are no wires or circuitry to go haywire. No LEDs, no little lights...it's just a basic, functional, solid mod.
Electronic Cigarette - Starter Kits - Telescope They are also at Hoosier's e-cig Supply and Madvapes.