It depends on use and
juice, but I think most tend to average around a week. I get about 2 weeks using 75pg/25vg and 80/20 when I was using them on the ego (3.4volt) batt's. I just started to use them at a higher voltage now on a Provari, so I don't know if that will change. Some of the signs will be a tighter draw on them, bad flavor, getting more
juice in your mouth when drawing. You can also look through the center tube and if you can't see through it it is usually done from what I know. Some people also clean them and can extend the life further. I myself do not bother with cleaning them, but I may do that to a few I have to clear some
juice that I did not like from them.