This is my solution to those situations that call for discretion. It is a Screwdriver Keychain battery with a 306 atty. I know that there is a risk when dripping on open batteries. In the month that I have been using this set up, I haven't had any trouble. It isn't like this is my all day vape. I use it when I have to be sneaky. If I know I'm going to be tied up somewhere that isn't vape friendly, I throw this in my pocket with a 3mil bottle of 54mg flavorless VG juice. On drop and one toke is all you need to be set for awhile. The flavorless juice leaves no odor and one good toke of the 54mg will kill the craving for some time.
Here are some size comparison pics of it in my hand, next to a 30mil bottle, and in between a Provari and a small Ego battery.

Here are some size comparison pics of it in my hand, next to a 30mil bottle, and in between a Provari and a small Ego battery.

on this subject.