I am on day 2 of using the e-cig, and haven't smoke a cigarette since started. I purchased the SmokeTip starter pack and am on my 3rd cartridge already. I am not sure how to exactly tell when the cartridge is empty, but I am guessing that it simply is when the flavor is nearly none existent. Also I am currious if I can refil the cartridges that come with the actual kit, and where a good place would be to find cheap tobacco flavored refills.