So it looks like hana modz are trying to take on the vapor flask with their latest Dna 40 device. The v4.d - a dual 18650 device.
More info here http://www.hanamodz.com/dna40dualbattery
and here is a size comparison
More info here http://www.hanamodz.com/dna40dualbattery
and here is a size comparison