I'm still fairly new to vaping - my question is: typically, how long should a cartridge last before having to add more juice? I use a M401 and just ordered blank cartridges - added about 6 or 7 drops of juice and for the first time in 3 months or so - I found the cartridge lasted a good long time before I had to add more juice. Typically, I found myself adding juice every time I used it.