I am still a bit confused. Can you buy blank RN4081 cartomizers that work with the Smokestik batteries (I have a Hendu)? I am looking for blank units to fill with ejiuce, but use my SS battery. I assume an RN4081 has a different internal design than the prefilled SS cartomizers? Which is better - using up a SS cartomizer, then refilling it, or trying to buy a blank?