The 2 coils (burners) provide the cartomizer with extra flavor and vaping. Then it's a good thing that you enjoy the throat hit.
Here you can buy 1 pc of dual coil 2.5 Ohm cartomizer (see photo on the left):
Soft rubber tip
It contains 2.5 - 3.5 ml of eliquid
Height: 74 mm with a 'tip' without tip 55 mm
Diameter: 10 mm
The cartomizer tube will not last forever. This will depend on how much heat it generates and, with time, it will crack at the bottom. How long this will take may vary a lot. But the positive thing is that it will not leak since the filter is highly absorbent, maintaining the liquid inside the tube.