The 2 coils (burners) provide the cartomizer with extra flavor and vape. Then it's a good thing that you enjoy the throat scratch.
Here you can buy 1 pc of dual coil 2.5 Ohm cartomizer (see photo on the left):
contains 5 - 5.5ml of smoking liquid
height: 74 mm with 'tip' without tip 55 mm
diameter: 10 mm
The cartomizer tube will not last forever. This will depend on how high heat it generates and, with time, it will crack at the bottom. How long this will take varies a lot. But the positive thing is that it will not leak since the filter is highly absorbent maintaining the liquid inside the tube.