depends on too many variables for me to give an accurate answer for you
im a light smoker so i generally get a full day with no problem (as long as the atomizer holds up) at night i top it off with 2-4 drops, and repeat the next day until the atomizer starts shitting out on me (some last significantly longer than others) then i toss it and start on a new one
without topping off the carts i get about a day and a half out of them
YMMV
battery life is more of an issue for me than cartridge life... i usually go through one battery during the day, then start on the second at night when i go for coffee... some times the battery will last all day and night, some times the battery will die stupidly fast and i need to start on the second one half way through the day, meaning i will need to get the first one charged either at work or as soon as i get home (i need to get a usb power adapter for the car)
again this will all vary for you, based on what model you were to get, how much you use it, etc...