I'm personally not a fan of the cigalikes. You might want to stick with a smaller mod that still uses a replaceable battery. My favorite device to use for stealth (ie at the cinema) is the Smoktech Gripper.
It's only $16, $4 more for the extension which enables you to use any other juice delivery device like a clearomizer, cartotank, etc. For the smaller profile look, any XL (45mm) cartomizer fits inside the mod body for a smaller form factor; just add a drip tip on top.
It uses an 18350 battery which can give you at least 7 hours of use; the batteries are small enough to carry a spare easily if you need more time than that. Available at Got Vapes and Mad Vapes.
Gripper and the extender.