I have Boge 3.0's lasting about a 7 days at 4.7v, if it's the only carto you are using. 1.5 Dual Coils can last around 2 weeks at 3.7v as your only vape. I start to notice the draw getting tighter, and the flavor gets muted. Just all according to what you are using. I trade off stuff all the time though, usually keeping 3 tanks going at once, and I usually get about 20 - 30 mil vaped before they go tight and weird.