After you have vaped for a while and have used up a bit of the liquid in the cartridge you need to add more. I do not care what anyone says, those cartridges do NOT hold two full packs of cigarettes! At the most I place about 15 drops of e-liquid into an empty cartridge and that is equal to approximately 4 cigarettes. When I first started vaping I did a lot of research and went to every page that would give me information. It soon became clear that everyone who was just trying to help newbies learn how to use their new e-cig were the ones with the best and most accurate information. That is how I learned that 3 drops of e-liquid is approximately one analog cigarette. If a cartridge holds 21 drops of e-liquid then you are looking at 7 cigarettes at best and not two packs. Unless you are using a cartomizer, you will not use 21 drops of e-liquid. The worst thing you can do to your atomizer is to vape it while it is dry. Not only does it taste bad to vape it when it is dry but it will burn up your atomizer as well. Don’t put 15 drops of e-liquid into a cartridge and expect it to last you all day. Carry a little bottle of liquid with you everywhere you go!