What e-cig are you using? And by cartridge do you really mean cartridge aka cart, the push on mouth part of a 3-piece e-cig? Or do you mean cartomizer aka carto, the screw-on mouth part of a 2-piece e-cig?
Slick rebranders on the web totally lie about how long a cartomizer lasts. Rebranders often say a cartomizer (they may call it cart) lasts as long as 1 pack or even 1 1/2 packs of cigarettes. But that is just a lie for them to sell their stuff. The Chinese manufacturers lie too in their specs. They say things like you get 200-300 puffs per cart which is just ridiculously wrong unless the Chinese are figuring in refills.
That's why you want a model with carts or cartos you can refill easily with e-liquid. The screw-on cartomizers are meant to be disposable but if you don't burn them dry you can get some number of refills out of them until you either singe the stuffing, or the internal atty dies, or it just tastes bad. Rebrander 2-piece e-cigs often have harder to fill cartos with hard caps or glued on caps because they want you to buy lots from them, not refill them (it is still possible to refill them, just not the intended way if you can't get the mouth-end cap off without mangling it). For popular models like those recommended here, you can get soft-cap cartos that are more easily refilled. You might get 5-8 cigarette's worth or puffs out of cartomizer I think?
Re the carts - the push on carts of 2-piece e-cigs - many of those hold about 1/2 as much as a normal size carto. You might get 2-5 cigarettes worth of puffs out of one but then they can be topped off the e-liquid or totally refilled, the stuffing can be replaced when it gets cranky, etc.
